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author | Georg Brandl <georg@python.org> | 2007-08-15 14:26:55 (GMT) |
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committer | Georg Brandl <georg@python.org> | 2007-08-15 14:26:55 (GMT) |
commit | f56181ff53ba00b7bed3997a4dccd9a1b6217b57 (patch) | |
tree | 1200947a7ffc78c2719831e4c7fd900a8ab01368 /Doc/ext | |
parent | af62d9abfb78067a54c769302005f952ed999f6a (diff) | |
download | cpython-f56181ff53ba00b7bed3997a4dccd9a1b6217b57.zip cpython-f56181ff53ba00b7bed3997a4dccd9a1b6217b57.tar.gz cpython-f56181ff53ba00b7bed3997a4dccd9a1b6217b57.tar.bz2 |
Delete the LaTeX doc tree.
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-rw-r--r-- | Doc/ext/embedding.tex | 316 | ||||
-rw-r--r-- | Doc/ext/ext.tex | 67 | ||||
-rw-r--r-- | Doc/ext/extending.tex | 1390 | ||||
-rw-r--r-- | Doc/ext/newtypes.tex | 1765 | ||||
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-rw-r--r-- | Doc/ext/run-func.c | 68 | ||||
-rw-r--r-- | Doc/ext/setup.py | 8 | ||||
-rw-r--r-- | Doc/ext/shoddy.c | 91 | ||||
-rw-r--r-- | Doc/ext/test.py | 213 | ||||
-rw-r--r-- | Doc/ext/windows.tex | 320 |
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diff --git a/Doc/ext/building.tex b/Doc/ext/building.tex deleted file mode 100644 index 42384c1..0000000 --- a/Doc/ext/building.tex +++ /dev/null @@ -1,143 +0,0 @@ -\chapter{Building C and \Cpp{} Extensions with distutils - \label{building}} - -\sectionauthor{Martin v. L\"owis}{martin@v.loewis.de} - -Starting in Python 1.4, Python provides, on \UNIX{}, a special make -file for building make files for building dynamically-linked -extensions and custom interpreters. Starting with Python 2.0, this -mechanism (known as related to Makefile.pre.in, and Setup files) is no -longer supported. Building custom interpreters was rarely used, and -extension modules can be built using distutils. - -Building an extension module using distutils requires that distutils -is installed on the build machine, which is included in Python 2.x and -available separately for Python 1.5. Since distutils also supports -creation of binary packages, users don't necessarily need a compiler -and distutils to install the extension. - -A distutils package contains a driver script, \file{setup.py}. This is -a plain Python file, which, in the most simple case, could look like -this: - -\begin{verbatim} -from distutils.core import setup, Extension - -module1 = Extension('demo', - sources = ['demo.c']) - -setup (name = 'PackageName', - version = '1.0', - description = 'This is a demo package', - ext_modules = [module1]) - -\end{verbatim} - -With this \file{setup.py}, and a file \file{demo.c}, running - -\begin{verbatim} -python setup.py build -\end{verbatim} - -will compile \file{demo.c}, and produce an extension module named -\samp{demo} in the \file{build} directory. Depending on the system, -the module file will end up in a subdirectory \file{build/lib.system}, -and may have a name like \file{demo.so} or \file{demo.pyd}. - -In the \file{setup.py}, all execution is performed by calling the -\samp{setup} function. This takes a variable number of keyword -arguments, of which the example above uses only a -subset. Specifically, the example specifies meta-information to build -packages, and it specifies the contents of the package. Normally, a -package will contain of addition modules, like Python source modules, -documentation, subpackages, etc. Please refer to the distutils -documentation in \citetitle[../dist/dist.html]{Distributing Python -Modules} to learn more about the features of distutils; this section -explains building extension modules only. - -It is common to pre-compute arguments to \function{setup}, to better -structure the driver script. In the example above, -the\samp{ext_modules} argument to \function{setup} is a list of -extension modules, each of which is an instance of the -\class{Extension}. In the example, the instance defines an extension -named \samp{demo} which is build by compiling a single source file, -\file{demo.c}. - -In many cases, building an extension is more complex, since additional -preprocessor defines and libraries may be needed. This is demonstrated -in the example below. - -\begin{verbatim} -from distutils.core import setup, Extension - -module1 = Extension('demo', - define_macros = [('MAJOR_VERSION', '1'), - ('MINOR_VERSION', '0')], - include_dirs = ['/usr/local/include'], - libraries = ['tcl83'], - library_dirs = ['/usr/local/lib'], - sources = ['demo.c']) - -setup (name = 'PackageName', - version = '1.0', - description = 'This is a demo package', - author = 'Martin v. Loewis', - author_email = 'martin@v.loewis.de', - url = 'http://www.python.org/doc/current/ext/building.html', - long_description = ''' -This is really just a demo package. -''', - ext_modules = [module1]) - -\end{verbatim} - -In this example, \function{setup} is called with additional -meta-information, which is recommended when distribution packages have -to be built. For the extension itself, it specifies preprocessor -defines, include directories, library directories, and libraries. -Depending on the compiler, distutils passes this information in -different ways to the compiler. For example, on \UNIX{}, this may -result in the compilation commands - -\begin{verbatim} -gcc -DNDEBUG -g -O3 -Wall -Wstrict-prototypes -fPIC -DMAJOR_VERSION=1 -DMINOR_VERSION=0 -I/usr/local/include -I/usr/local/include/python2.2 -c demo.c -o build/temp.linux-i686-2.2/demo.o - -gcc -shared build/temp.linux-i686-2.2/demo.o -L/usr/local/lib -ltcl83 -o build/lib.linux-i686-2.2/demo.so -\end{verbatim} - -These lines are for demonstration purposes only; distutils users -should trust that distutils gets the invocations right. - -\section{Distributing your extension modules - \label{distributing}} - -When an extension has been successfully build, there are three ways to -use it. - -End-users will typically want to install the module, they do so by -running - -\begin{verbatim} -python setup.py install -\end{verbatim} - -Module maintainers should produce source packages; to do so, they run - -\begin{verbatim} -python setup.py sdist -\end{verbatim} - -In some cases, additional files need to be included in a source -distribution; this is done through a \file{MANIFEST.in} file; see the -distutils documentation for details. - -If the source distribution has been build successfully, maintainers -can also create binary distributions. Depending on the platform, one -of the following commands can be used to do so. - -\begin{verbatim} -python setup.py bdist_wininst -python setup.py bdist_rpm -python setup.py bdist_dumb -\end{verbatim} - diff --git a/Doc/ext/embedding.tex b/Doc/ext/embedding.tex deleted file mode 100644 index 58ec5ca..0000000 --- a/Doc/ext/embedding.tex +++ /dev/null @@ -1,316 +0,0 @@ -\chapter{Embedding Python in Another Application - \label{embedding}} - -The previous chapters discussed how to extend Python, that is, how to -extend the functionality of Python by attaching a library of C -functions to it. It is also possible to do it the other way around: -enrich your C/\Cpp{} application by embedding Python in it. Embedding -provides your application with the ability to implement some of the -functionality of your application in Python rather than C or \Cpp. -This can be used for many purposes; one example would be to allow -users to tailor the application to their needs by writing some scripts -in Python. You can also use it yourself if some of the functionality -can be written in Python more easily. - -Embedding Python is similar to extending it, but not quite. The -difference is that when you extend Python, the main program of the -application is still the Python interpreter, while if you embed -Python, the main program may have nothing to do with Python --- -instead, some parts of the application occasionally call the Python -interpreter to run some Python code. - -So if you are embedding Python, you are providing your own main -program. One of the things this main program has to do is initialize -the Python interpreter. At the very least, you have to call the -function \cfunction{Py_Initialize()} (on Mac OS, call -\cfunction{PyMac_Initialize()} instead). There are optional calls to -pass command line arguments to Python. Then later you can call the -interpreter from any part of the application. - -There are several different ways to call the interpreter: you can pass -a string containing Python statements to -\cfunction{PyRun_SimpleString()}, or you can pass a stdio file pointer -and a file name (for identification in error messages only) to -\cfunction{PyRun_SimpleFile()}. You can also call the lower-level -operations described in the previous chapters to construct and use -Python objects. - -A simple demo of embedding Python can be found in the directory -\file{Demo/embed/} of the source distribution. - - -\begin{seealso} - \seetitle[../api/api.html]{Python/C API Reference Manual}{The - details of Python's C interface are given in this manual. - A great deal of necessary information can be found here.} -\end{seealso} - - -\section{Very High Level Embedding - \label{high-level-embedding}} - -The simplest form of embedding Python is the use of the very -high level interface. This interface is intended to execute a -Python script without needing to interact with the application -directly. This can for example be used to perform some operation -on a file. - -\begin{verbatim} -#include <Python.h> - -int -main(int argc, char *argv[]) -{ - Py_Initialize(); - PyRun_SimpleString("from time import time,ctime\n" - "print 'Today is',ctime(time())\n"); - Py_Finalize(); - return 0; -} -\end{verbatim} - -The above code first initializes the Python interpreter with -\cfunction{Py_Initialize()}, followed by the execution of a hard-coded -Python script that print the date and time. Afterwards, the -\cfunction{Py_Finalize()} call shuts the interpreter down, followed by -the end of the program. In a real program, you may want to get the -Python script from another source, perhaps a text-editor routine, a -file, or a database. Getting the Python code from a file can better -be done by using the \cfunction{PyRun_SimpleFile()} function, which -saves you the trouble of allocating memory space and loading the file -contents. - - -\section{Beyond Very High Level Embedding: An overview - \label{lower-level-embedding}} - -The high level interface gives you the ability to execute -arbitrary pieces of Python code from your application, but -exchanging data values is quite cumbersome to say the least. If -you want that, you should use lower level calls. At the cost of -having to write more C code, you can achieve almost anything. - -It should be noted that extending Python and embedding Python -is quite the same activity, despite the different intent. Most -topics discussed in the previous chapters are still valid. To -show this, consider what the extension code from Python to C -really does: - -\begin{enumerate} - \item Convert data values from Python to C, - \item Perform a function call to a C routine using the - converted values, and - \item Convert the data values from the call from C to Python. -\end{enumerate} - -When embedding Python, the interface code does: - -\begin{enumerate} - \item Convert data values from C to Python, - \item Perform a function call to a Python interface routine - using the converted values, and - \item Convert the data values from the call from Python to C. -\end{enumerate} - -As you can see, the data conversion steps are simply swapped to -accommodate the different direction of the cross-language transfer. -The only difference is the routine that you call between both -data conversions. When extending, you call a C routine, when -embedding, you call a Python routine. - -This chapter will not discuss how to convert data from Python -to C and vice versa. Also, proper use of references and dealing -with errors is assumed to be understood. Since these aspects do not -differ from extending the interpreter, you can refer to earlier -chapters for the required information. - - -\section{Pure Embedding - \label{pure-embedding}} - -The first program aims to execute a function in a Python -script. Like in the section about the very high level interface, -the Python interpreter does not directly interact with the -application (but that will change in the next section). - -The code to run a function defined in a Python script is: - -\verbatiminput{run-func.c} - -This code loads a Python script using \code{argv[1]}, and calls the -function named in \code{argv[2]}. Its integer arguments are the other -values of the \code{argv} array. If you compile and link this -program (let's call the finished executable \program{call}), and use -it to execute a Python script, such as: - -\begin{verbatim} -def multiply(a,b): - print "Will compute", a, "times", b - c = 0 - for i in range(0, a): - c = c + b - return c -\end{verbatim} - -then the result should be: - -\begin{verbatim} -$ call multiply multiply 3 2 -Will compute 3 times 2 -Result of call: 6 -\end{verbatim} % $ - -Although the program is quite large for its functionality, most of the -code is for data conversion between Python and C, and for error -reporting. The interesting part with respect to embedding Python -starts with - -\begin{verbatim} - Py_Initialize(); - pName = PyString_FromString(argv[1]); - /* Error checking of pName left out */ - pModule = PyImport_Import(pName); -\end{verbatim} - -After initializing the interpreter, the script is loaded using -\cfunction{PyImport_Import()}. This routine needs a Python string -as its argument, which is constructed using the -\cfunction{PyString_FromString()} data conversion routine. - -\begin{verbatim} - pFunc = PyObject_GetAttrString(pModule, argv[2]); - /* pFunc is a new reference */ - - if (pFunc && PyCallable_Check(pFunc)) { - ... - } - Py_XDECREF(pFunc); -\end{verbatim} - -Once the script is loaded, the name we're looking for is retrieved -using \cfunction{PyObject_GetAttrString()}. If the name exists, and -the object returned is callable, you can safely assume that it is a -function. The program then proceeds by constructing a tuple of -arguments as normal. The call to the Python function is then made -with: - -\begin{verbatim} - pValue = PyObject_CallObject(pFunc, pArgs); -\end{verbatim} - -Upon return of the function, \code{pValue} is either \NULL{} or it -contains a reference to the return value of the function. Be sure to -release the reference after examining the value. - - -\section{Extending Embedded Python - \label{extending-with-embedding}} - -Until now, the embedded Python interpreter had no access to -functionality from the application itself. The Python API allows this -by extending the embedded interpreter. That is, the embedded -interpreter gets extended with routines provided by the application. -While it sounds complex, it is not so bad. Simply forget for a while -that the application starts the Python interpreter. Instead, consider -the application to be a set of subroutines, and write some glue code -that gives Python access to those routines, just like you would write -a normal Python extension. For example: - -\begin{verbatim} -static int numargs=0; - -/* Return the number of arguments of the application command line */ -static PyObject* -emb_numargs(PyObject *self, PyObject *args) -{ - if(!PyArg_ParseTuple(args, ":numargs")) - return NULL; - return Py_BuildValue("i", numargs); -} - -static PyMethodDef EmbMethods[] = { - {"numargs", emb_numargs, METH_VARARGS, - "Return the number of arguments received by the process."}, - {NULL, NULL, 0, NULL} -}; -\end{verbatim} - -Insert the above code just above the \cfunction{main()} function. -Also, insert the following two statements directly after -\cfunction{Py_Initialize()}: - -\begin{verbatim} - numargs = argc; - Py_InitModule("emb", EmbMethods); -\end{verbatim} - -These two lines initialize the \code{numargs} variable, and make the -\function{emb.numargs()} function accessible to the embedded Python -interpreter. With these extensions, the Python script can do things -like - -\begin{verbatim} -import emb -print "Number of arguments", emb.numargs() -\end{verbatim} - -In a real application, the methods will expose an API of the -application to Python. - - -%\section{For the future} -% -%You don't happen to have a nice library to get textual -%equivalents of numeric values do you :-) ? -%Callbacks here ? (I may be using information from that section -%?!) -%threads -%code examples do not really behave well if errors happen -% (what to watch out for) - - -\section{Embedding Python in \Cpp - \label{embeddingInCplusplus}} - -It is also possible to embed Python in a \Cpp{} program; precisely how this -is done will depend on the details of the \Cpp{} system used; in general you -will need to write the main program in \Cpp, and use the \Cpp{} compiler -to compile and link your program. There is no need to recompile Python -itself using \Cpp. - - -\section{Linking Requirements - \label{link-reqs}} - -While the \program{configure} script shipped with the Python sources -will correctly build Python to export the symbols needed by -dynamically linked extensions, this is not automatically inherited by -applications which embed the Python library statically, at least on -\UNIX. This is an issue when the application is linked to the static -runtime library (\file{libpython.a}) and needs to load dynamic -extensions (implemented as \file{.so} files). - -The problem is that some entry points are defined by the Python -runtime solely for extension modules to use. If the embedding -application does not use any of these entry points, some linkers will -not include those entries in the symbol table of the finished -executable. Some additional options are needed to inform the linker -not to remove these symbols. - -Determining the right options to use for any given platform can be -quite difficult, but fortunately the Python configuration already has -those values. To retrieve them from an installed Python interpreter, -start an interactive interpreter and have a short session like this: - -\begin{verbatim} ->>> import distutils.sysconfig ->>> distutils.sysconfig.get_config_var('LINKFORSHARED') -'-Xlinker -export-dynamic' -\end{verbatim} -\refstmodindex{distutils.sysconfig} - -The contents of the string presented will be the options that should -be used. If the string is empty, there's no need to add any -additional options. The \constant{LINKFORSHARED} definition -corresponds to the variable of the same name in Python's top-level -\file{Makefile}. diff --git a/Doc/ext/ext.tex b/Doc/ext/ext.tex deleted file mode 100644 index b4130d1..0000000 --- a/Doc/ext/ext.tex +++ /dev/null @@ -1,67 +0,0 @@ -\documentclass{manual} - -% XXX PM explain how to add new types to Python - -\title{Extending and Embedding the Python Interpreter} - -\input{boilerplate} - -% Tell \index to actually write the .idx file -\makeindex - -\begin{document} - -\maketitle - -\ifhtml -\chapter*{Front Matter\label{front}} -\fi - -\input{copyright} - - -\begin{abstract} - -\noindent -Python is an interpreted, object-oriented programming language. This -document describes how to write modules in C or \Cpp{} to extend the -Python interpreter with new modules. Those modules can define new -functions but also new object types and their methods. The document -also describes how to embed the Python interpreter in another -application, for use as an extension language. Finally, it shows how -to compile and link extension modules so that they can be loaded -dynamically (at run time) into the interpreter, if the underlying -operating system supports this feature. - -This document assumes basic knowledge about Python. For an informal -introduction to the language, see the -\citetitle[../tut/tut.html]{Python Tutorial}. The -\citetitle[../ref/ref.html]{Python Reference Manual} gives a more -formal definition of the language. The -\citetitle[../lib/lib.html]{Python Library Reference} documents the -existing object types, functions and modules (both built-in and -written in Python) that give the language its wide application range. - -For a detailed description of the whole Python/C API, see the separate -\citetitle[../api/api.html]{Python/C API Reference Manual}. - -\end{abstract} - -\tableofcontents - - -\input{extending} -\input{newtypes} -\input{building} -\input{windows} -\input{embedding} - - -\appendix -\chapter{Reporting Bugs} -\input{reportingbugs} - -\chapter{History and License} -\input{license} - -\end{document} diff --git a/Doc/ext/extending.tex b/Doc/ext/extending.tex deleted file mode 100644 index 53d90db..0000000 --- a/Doc/ext/extending.tex +++ /dev/null @@ -1,1390 +0,0 @@ -\chapter{Extending Python with \C{} or \Cpp{} \label{intro}} - - -It is quite easy to add new built-in modules to Python, if you know -how to program in C. Such \dfn{extension modules} can do two things -that can't be done directly in Python: they can implement new built-in -object types, and they can call C library functions and system calls. - -To support extensions, the Python API (Application Programmers -Interface) defines a set of functions, macros and variables that -provide access to most aspects of the Python run-time system. The -Python API is incorporated in a C source file by including the header -\code{"Python.h"}. - -The compilation of an extension module depends on its intended use as -well as on your system setup; details are given in later chapters. - - -\section{A Simple Example - \label{simpleExample}} - -Let's create an extension module called \samp{spam} (the favorite food -of Monty Python fans...) and let's say we want to create a Python -interface to the C library function \cfunction{system()}.\footnote{An -interface for this function already exists in the standard module -\module{os} --- it was chosen as a simple and straightforward example.} -This function takes a null-terminated character string as argument and -returns an integer. We want this function to be callable from Python -as follows: - -\begin{verbatim} ->>> import spam ->>> status = spam.system("ls -l") -\end{verbatim} - -Begin by creating a file \file{spammodule.c}. (Historically, if a -module is called \samp{spam}, the C file containing its implementation -is called \file{spammodule.c}; if the module name is very long, like -\samp{spammify}, the module name can be just \file{spammify.c}.) - -The first line of our file can be: - -\begin{verbatim} -#include <Python.h> -\end{verbatim} - -which pulls in the Python API (you can add a comment describing the -purpose of the module and a copyright notice if you like). - -\begin{notice}[warning] - Since Python may define some pre-processor definitions which affect - the standard headers on some systems, you \emph{must} include - \file{Python.h} before any standard headers are included. -\end{notice} - -All user-visible symbols defined by \file{Python.h} have a prefix of -\samp{Py} or \samp{PY}, except those defined in standard header files. -For convenience, and since they are used extensively by the Python -interpreter, \code{"Python.h"} includes a few standard header files: -\code{<stdio.h>}, \code{<string.h>}, \code{<errno.h>}, and -\code{<stdlib.h>}. If the latter header file does not exist on your -system, it declares the functions \cfunction{malloc()}, -\cfunction{free()} and \cfunction{realloc()} directly. - -The next thing we add to our module file is the C function that will -be called when the Python expression \samp{spam.system(\var{string})} -is evaluated (we'll see shortly how it ends up being called): - -\begin{verbatim} -static PyObject * -spam_system(PyObject *self, PyObject *args) -{ - const char *command; - int sts; - - if (!PyArg_ParseTuple(args, "s", &command)) - return NULL; - sts = system(command); - return Py_BuildValue("i", sts); -} -\end{verbatim} - -There is a straightforward translation from the argument list in -Python (for example, the single expression \code{"ls -l"}) to the -arguments passed to the C function. The C function always has two -arguments, conventionally named \var{self} and \var{args}. - -The \var{self} argument is only used when the C function implements a -built-in method, not a function. In the example, \var{self} will -always be a \NULL{} pointer, since we are defining a function, not a -method. (This is done so that the interpreter doesn't have to -understand two different types of C functions.) - -The \var{args} argument will be a pointer to a Python tuple object -containing the arguments. Each item of the tuple corresponds to an -argument in the call's argument list. The arguments are Python -objects --- in order to do anything with them in our C function we have -to convert them to C values. The function \cfunction{PyArg_ParseTuple()} -in the Python API checks the argument types and converts them to C -values. It uses a template string to determine the required types of -the arguments as well as the types of the C variables into which to -store the converted values. More about this later. - -\cfunction{PyArg_ParseTuple()} returns true (nonzero) if all arguments have -the right type and its components have been stored in the variables -whose addresses are passed. It returns false (zero) if an invalid -argument list was passed. In the latter case it also raises an -appropriate exception so the calling function can return -\NULL{} immediately (as we saw in the example). - - -\section{Intermezzo: Errors and Exceptions - \label{errors}} - -An important convention throughout the Python interpreter is the -following: when a function fails, it should set an exception condition -and return an error value (usually a \NULL{} pointer). Exceptions -are stored in a static global variable inside the interpreter; if this -variable is \NULL{} no exception has occurred. A second global -variable stores the ``associated value'' of the exception (the second -argument to \keyword{raise}). A third variable contains the stack -traceback in case the error originated in Python code. These three -variables are the C equivalents of the Python variables -\code{sys.exc_type}, \code{sys.exc_value} and \code{sys.exc_traceback} (see -the section on module \module{sys} in the -\citetitle[../lib/lib.html]{Python Library Reference}). It is -important to know about them to understand how errors are passed -around. - -The Python API defines a number of functions to set various types of -exceptions. - -The most common one is \cfunction{PyErr_SetString()}. Its arguments -are an exception object and a C string. The exception object is -usually a predefined object like \cdata{PyExc_ZeroDivisionError}. The -C string indicates the cause of the error and is converted to a -Python string object and stored as the ``associated value'' of the -exception. - -Another useful function is \cfunction{PyErr_SetFromErrno()}, which only -takes an exception argument and constructs the associated value by -inspection of the global variable \cdata{errno}. The most -general function is \cfunction{PyErr_SetObject()}, which takes two object -arguments, the exception and its associated value. You don't need to -\cfunction{Py_INCREF()} the objects passed to any of these functions. - -You can test non-destructively whether an exception has been set with -\cfunction{PyErr_Occurred()}. This returns the current exception object, -or \NULL{} if no exception has occurred. You normally don't need -to call \cfunction{PyErr_Occurred()} to see whether an error occurred in a -function call, since you should be able to tell from the return value. - -When a function \var{f} that calls another function \var{g} detects -that the latter fails, \var{f} should itself return an error value -(usually \NULL{} or \code{-1}). It should \emph{not} call one of the -\cfunction{PyErr_*()} functions --- one has already been called by \var{g}. -\var{f}'s caller is then supposed to also return an error indication -to \emph{its} caller, again \emph{without} calling \cfunction{PyErr_*()}, -and so on --- the most detailed cause of the error was already -reported by the function that first detected it. Once the error -reaches the Python interpreter's main loop, this aborts the currently -executing Python code and tries to find an exception handler specified -by the Python programmer. - -(There are situations where a module can actually give a more detailed -error message by calling another \cfunction{PyErr_*()} function, and in -such cases it is fine to do so. As a general rule, however, this is -not necessary, and can cause information about the cause of the error -to be lost: most operations can fail for a variety of reasons.) - -To ignore an exception set by a function call that failed, the exception -condition must be cleared explicitly by calling \cfunction{PyErr_Clear()}. -The only time C code should call \cfunction{PyErr_Clear()} is if it doesn't -want to pass the error on to the interpreter but wants to handle it -completely by itself (possibly by trying something else, or pretending -nothing went wrong). - -Every failing \cfunction{malloc()} call must be turned into an -exception --- the direct caller of \cfunction{malloc()} (or -\cfunction{realloc()}) must call \cfunction{PyErr_NoMemory()} and -return a failure indicator itself. All the object-creating functions -(for example, \cfunction{PyInt_FromLong()}) already do this, so this -note is only relevant to those who call \cfunction{malloc()} directly. - -Also note that, with the important exception of -\cfunction{PyArg_ParseTuple()} and friends, functions that return an -integer status usually return a positive value or zero for success and -\code{-1} for failure, like \UNIX{} system calls. - -Finally, be careful to clean up garbage (by making -\cfunction{Py_XDECREF()} or \cfunction{Py_DECREF()} calls for objects -you have already created) when you return an error indicator! - -The choice of which exception to raise is entirely yours. There are -predeclared C objects corresponding to all built-in Python exceptions, -such as \cdata{PyExc_ZeroDivisionError}, which you can use directly. -Of course, you should choose exceptions wisely --- don't use -\cdata{PyExc_TypeError} to mean that a file couldn't be opened (that -should probably be \cdata{PyExc_IOError}). If something's wrong with -the argument list, the \cfunction{PyArg_ParseTuple()} function usually -raises \cdata{PyExc_TypeError}. If you have an argument whose value -must be in a particular range or must satisfy other conditions, -\cdata{PyExc_ValueError} is appropriate. - -You can also define a new exception that is unique to your module. -For this, you usually declare a static object variable at the -beginning of your file: - -\begin{verbatim} -static PyObject *SpamError; -\end{verbatim} - -and initialize it in your module's initialization function -(\cfunction{initspam()}) with an exception object (leaving out -the error checking for now): - -\begin{verbatim} -PyMODINIT_FUNC -initspam(void) -{ - PyObject *m; - - m = Py_InitModule("spam", SpamMethods); - if (m == NULL) - return; - - SpamError = PyErr_NewException("spam.error", NULL, NULL); - Py_INCREF(SpamError); - PyModule_AddObject(m, "error", SpamError); -} -\end{verbatim} - -Note that the Python name for the exception object is -\exception{spam.error}. The \cfunction{PyErr_NewException()} function -may create a class with the base class being \exception{Exception} -(unless another class is passed in instead of \NULL), described in the -\citetitle[../lib/lib.html]{Python Library Reference} under ``Built-in -Exceptions.'' - -Note also that the \cdata{SpamError} variable retains a reference to -the newly created exception class; this is intentional! Since the -exception could be removed from the module by external code, an owned -reference to the class is needed to ensure that it will not be -discarded, causing \cdata{SpamError} to become a dangling pointer. -Should it become a dangling pointer, C code which raises the exception -could cause a core dump or other unintended side effects. - -We discuss the use of PyMODINIT_FUNC as a function return type later in this -sample. - -\section{Back to the Example - \label{backToExample}} - -Going back to our example function, you should now be able to -understand this statement: - -\begin{verbatim} - if (!PyArg_ParseTuple(args, "s", &command)) - return NULL; -\end{verbatim} - -It returns \NULL{} (the error indicator for functions returning -object pointers) if an error is detected in the argument list, relying -on the exception set by \cfunction{PyArg_ParseTuple()}. Otherwise the -string value of the argument has been copied to the local variable -\cdata{command}. This is a pointer assignment and you are not supposed -to modify the string to which it points (so in Standard C, the variable -\cdata{command} should properly be declared as \samp{const char -*command}). - -The next statement is a call to the \UNIX{} function -\cfunction{system()}, passing it the string we just got from -\cfunction{PyArg_ParseTuple()}: - -\begin{verbatim} - sts = system(command); -\end{verbatim} - -Our \function{spam.system()} function must return the value of -\cdata{sts} as a Python object. This is done using the function -\cfunction{Py_BuildValue()}, which is something like the inverse of -\cfunction{PyArg_ParseTuple()}: it takes a format string and an -arbitrary number of C values, and returns a new Python object. -More info on \cfunction{Py_BuildValue()} is given later. - -\begin{verbatim} - return Py_BuildValue("i", sts); -\end{verbatim} - -In this case, it will return an integer object. (Yes, even integers -are objects on the heap in Python!) - -If you have a C function that returns no useful argument (a function -returning \ctype{void}), the corresponding Python function must return -\code{None}. You need this idiom to do so (which is implemented by the -\csimplemacro{Py_RETURN_NONE} macro): - -\begin{verbatim} - Py_INCREF(Py_None); - return Py_None; -\end{verbatim} - -\cdata{Py_None} is the C name for the special Python object -\code{None}. It is a genuine Python object rather than a \NULL{} -pointer, which means ``error'' in most contexts, as we have seen. - - -\section{The Module's Method Table and Initialization Function - \label{methodTable}} - -I promised to show how \cfunction{spam_system()} is called from Python -programs. First, we need to list its name and address in a ``method -table'': - -\begin{verbatim} -static PyMethodDef SpamMethods[] = { - ... - {"system", spam_system, METH_VARARGS, - "Execute a shell command."}, - ... - {NULL, NULL, 0, NULL} /* Sentinel */ -}; -\end{verbatim} - -Note the third entry (\samp{METH_VARARGS}). This is a flag telling -the interpreter the calling convention to be used for the C -function. It should normally always be \samp{METH_VARARGS} or -\samp{METH_VARARGS | METH_KEYWORDS}; a value of \code{0} means that an -obsolete variant of \cfunction{PyArg_ParseTuple()} is used. - -When using only \samp{METH_VARARGS}, the function should expect -the Python-level parameters to be passed in as a tuple acceptable for -parsing via \cfunction{PyArg_ParseTuple()}; more information on this -function is provided below. - -The \constant{METH_KEYWORDS} bit may be set in the third field if -keyword arguments should be passed to the function. In this case, the -C function should accept a third \samp{PyObject *} parameter which -will be a dictionary of keywords. Use -\cfunction{PyArg_ParseTupleAndKeywords()} to parse the arguments to -such a function. - -The method table must be passed to the interpreter in the module's -initialization function. The initialization function must be named -\cfunction{init\var{name}()}, where \var{name} is the name of the -module, and should be the only non-\keyword{static} item defined in -the module file: - -\begin{verbatim} -PyMODINIT_FUNC -initspam(void) -{ - (void) Py_InitModule("spam", SpamMethods); -} -\end{verbatim} - -Note that PyMODINIT_FUNC declares the function as \code{void} return type, -declares any special linkage declarations required by the platform, and for -\Cpp{} declares the function as \code{extern "C"}. - -When the Python program imports module \module{spam} for the first -time, \cfunction{initspam()} is called. (See below for comments about -embedding Python.) It calls -\cfunction{Py_InitModule()}, which creates a ``module object'' (which -is inserted in the dictionary \code{sys.modules} under the key -\code{"spam"}), and inserts built-in function objects into the newly -created module based upon the table (an array of \ctype{PyMethodDef} -structures) that was passed as its second argument. -\cfunction{Py_InitModule()} returns a pointer to the module object -that it creates (which is unused here). It may abort with a fatal error -for certain errors, or return \NULL{} if the module could not be -initialized satisfactorily. - -When embedding Python, the \cfunction{initspam()} function is not -called automatically unless there's an entry in the -\cdata{_PyImport_Inittab} table. The easiest way to handle this is to -statically initialize your statically-linked modules by directly -calling \cfunction{initspam()} after the call to -\cfunction{Py_Initialize()}: - -\begin{verbatim} -int -main(int argc, char *argv[]) -{ - /* Pass argv[0] to the Python interpreter */ - Py_SetProgramName(argv[0]); - - /* Initialize the Python interpreter. Required. */ - Py_Initialize(); - - /* Add a static module */ - initspam(); -\end{verbatim} - -An example may be found in the file \file{Demo/embed/demo.c} in the -Python source distribution. - -\note{Removing entries from \code{sys.modules} or importing -compiled modules into multiple interpreters within a process (or -following a \cfunction{fork()} without an intervening -\cfunction{exec()}) can create problems for some extension modules. -Extension module authors should exercise caution when initializing -internal data structures. -Note also that the \function{reload()} function can be used with -extension modules, and will call the module initialization function -(\cfunction{initspam()} in the example), but will not load the module -again if it was loaded from a dynamically loadable object file -(\file{.so} on \UNIX, \file{.dll} on Windows).} - -A more substantial example module is included in the Python source -distribution as \file{Modules/xxmodule.c}. This file may be used as a -template or simply read as an example. The \program{modulator.py} -script included in the source distribution or Windows install provides -a simple graphical user interface for declaring the functions and -objects which a module should implement, and can generate a template -which can be filled in. The script lives in the -\file{Tools/modulator/} directory; see the \file{README} file there -for more information. - - -\section{Compilation and Linkage - \label{compilation}} - -There are two more things to do before you can use your new extension: -compiling and linking it with the Python system. If you use dynamic -loading, the details may depend on the style of dynamic loading your -system uses; see the chapters about building extension modules -(chapter \ref{building}) and additional information that pertains only -to building on Windows (chapter \ref{building-on-windows}) for more -information about this. - -If you can't use dynamic loading, or if you want to make your module a -permanent part of the Python interpreter, you will have to change the -configuration setup and rebuild the interpreter. Luckily, this is -very simple on \UNIX: just place your file (\file{spammodule.c} for -example) in the \file{Modules/} directory of an unpacked source -distribution, add a line to the file \file{Modules/Setup.local} -describing your file: - -\begin{verbatim} -spam spammodule.o -\end{verbatim} - -and rebuild the interpreter by running \program{make} in the toplevel -directory. You can also run \program{make} in the \file{Modules/} -subdirectory, but then you must first rebuild \file{Makefile} -there by running `\program{make} Makefile'. (This is necessary each -time you change the \file{Setup} file.) - -If your module requires additional libraries to link with, these can -be listed on the line in the configuration file as well, for instance: - -\begin{verbatim} -spam spammodule.o -lX11 -\end{verbatim} - -\section{Calling Python Functions from C - \label{callingPython}} - -So far we have concentrated on making C functions callable from -Python. The reverse is also useful: calling Python functions from C. -This is especially the case for libraries that support so-called -``callback'' functions. If a C interface makes use of callbacks, the -equivalent Python often needs to provide a callback mechanism to the -Python programmer; the implementation will require calling the Python -callback functions from a C callback. Other uses are also imaginable. - -Fortunately, the Python interpreter is easily called recursively, and -there is a standard interface to call a Python function. (I won't -dwell on how to call the Python parser with a particular string as -input --- if you're interested, have a look at the implementation of -the \programopt{-c} command line option in \file{Python/pythonmain.c} -from the Python source code.) - -Calling a Python function is easy. First, the Python program must -somehow pass you the Python function object. You should provide a -function (or some other interface) to do this. When this function is -called, save a pointer to the Python function object (be careful to -\cfunction{Py_INCREF()} it!) in a global variable --- or wherever you -see fit. For example, the following function might be part of a module -definition: - -\begin{verbatim} -static PyObject *my_callback = NULL; - -static PyObject * -my_set_callback(PyObject *dummy, PyObject *args) -{ - PyObject *result = NULL; - PyObject *temp; - - if (PyArg_ParseTuple(args, "O:set_callback", &temp)) { - if (!PyCallable_Check(temp)) { - PyErr_SetString(PyExc_TypeError, "parameter must be callable"); - return NULL; - } - Py_XINCREF(temp); /* Add a reference to new callback */ - Py_XDECREF(my_callback); /* Dispose of previous callback */ - my_callback = temp; /* Remember new callback */ - /* Boilerplate to return "None" */ - Py_INCREF(Py_None); - result = Py_None; - } - return result; -} -\end{verbatim} - -This function must be registered with the interpreter using the -\constant{METH_VARARGS} flag; this is described in section -\ref{methodTable}, ``The Module's Method Table and Initialization -Function.'' The \cfunction{PyArg_ParseTuple()} function and its -arguments are documented in section~\ref{parseTuple}, ``Extracting -Parameters in Extension Functions.'' - -The macros \cfunction{Py_XINCREF()} and \cfunction{Py_XDECREF()} -increment/decrement the reference count of an object and are safe in -the presence of \NULL{} pointers (but note that \var{temp} will not be -\NULL{} in this context). More info on them in -section~\ref{refcounts}, ``Reference Counts.'' - -Later, when it is time to call the function, you call the C function -\cfunction{PyEval_CallObject()}.\ttindex{PyEval_CallObject()} This -function has two arguments, both pointers to arbitrary Python objects: -the Python function, and the argument list. The argument list must -always be a tuple object, whose length is the number of arguments. To -call the Python function with no arguments, pass an empty tuple; to -call it with one argument, pass a singleton tuple. -\cfunction{Py_BuildValue()} returns a tuple when its format string -consists of zero or more format codes between parentheses. For -example: - -\begin{verbatim} - int arg; - PyObject *arglist; - PyObject *result; - ... - arg = 123; - ... - /* Time to call the callback */ - arglist = Py_BuildValue("(i)", arg); - result = PyEval_CallObject(my_callback, arglist); - Py_DECREF(arglist); -\end{verbatim} - -\cfunction{PyEval_CallObject()} returns a Python object pointer: this is -the return value of the Python function. \cfunction{PyEval_CallObject()} is -``reference-count-neutral'' with respect to its arguments. In the -example a new tuple was created to serve as the argument list, which -is \cfunction{Py_DECREF()}-ed immediately after the call. - -The return value of \cfunction{PyEval_CallObject()} is ``new'': either it -is a brand new object, or it is an existing object whose reference -count has been incremented. So, unless you want to save it in a -global variable, you should somehow \cfunction{Py_DECREF()} the result, -even (especially!) if you are not interested in its value. - -Before you do this, however, it is important to check that the return -value isn't \NULL. If it is, the Python function terminated by -raising an exception. If the C code that called -\cfunction{PyEval_CallObject()} is called from Python, it should now -return an error indication to its Python caller, so the interpreter -can print a stack trace, or the calling Python code can handle the -exception. If this is not possible or desirable, the exception should -be cleared by calling \cfunction{PyErr_Clear()}. For example: - -\begin{verbatim} - if (result == NULL) - return NULL; /* Pass error back */ - ...use result... - Py_DECREF(result); -\end{verbatim} - -Depending on the desired interface to the Python callback function, -you may also have to provide an argument list to -\cfunction{PyEval_CallObject()}. In some cases the argument list is -also provided by the Python program, through the same interface that -specified the callback function. It can then be saved and used in the -same manner as the function object. In other cases, you may have to -construct a new tuple to pass as the argument list. The simplest way -to do this is to call \cfunction{Py_BuildValue()}. For example, if -you want to pass an integral event code, you might use the following -code: - -\begin{verbatim} - PyObject *arglist; - ... - arglist = Py_BuildValue("(l)", eventcode); - result = PyEval_CallObject(my_callback, arglist); - Py_DECREF(arglist); - if (result == NULL) - return NULL; /* Pass error back */ - /* Here maybe use the result */ - Py_DECREF(result); -\end{verbatim} - -Note the placement of \samp{Py_DECREF(arglist)} immediately after the -call, before the error check! Also note that strictly spoken this -code is not complete: \cfunction{Py_BuildValue()} may run out of -memory, and this should be checked. - - -\section{Extracting Parameters in Extension Functions - \label{parseTuple}} - -\ttindex{PyArg_ParseTuple()} - -The \cfunction{PyArg_ParseTuple()} function is declared as follows: - -\begin{verbatim} -int PyArg_ParseTuple(PyObject *arg, char *format, ...); -\end{verbatim} - -The \var{arg} argument must be a tuple object containing an argument -list passed from Python to a C function. The \var{format} argument -must be a format string, whose syntax is explained in -``\ulink{Parsing arguments and building -values}{../api/arg-parsing.html}'' in the -\citetitle[../api/api.html]{Python/C API Reference Manual}. The -remaining arguments must be addresses of variables whose type is -determined by the format string. - -Note that while \cfunction{PyArg_ParseTuple()} checks that the Python -arguments have the required types, it cannot check the validity of the -addresses of C variables passed to the call: if you make mistakes -there, your code will probably crash or at least overwrite random bits -in memory. So be careful! - -Note that any Python object references which are provided to the -caller are \emph{borrowed} references; do not decrement their -reference count! - -Some example calls: - -\begin{verbatim} - int ok; - int i, j; - long k, l; - const char *s; - int size; - - ok = PyArg_ParseTuple(args, ""); /* No arguments */ - /* Python call: f() */ -\end{verbatim} - -\begin{verbatim} - ok = PyArg_ParseTuple(args, "s", &s); /* A string */ - /* Possible Python call: f('whoops!') */ -\end{verbatim} - -\begin{verbatim} - ok = PyArg_ParseTuple(args, "lls", &k, &l, &s); /* Two longs and a string */ - /* Possible Python call: f(1, 2, 'three') */ -\end{verbatim} - -\begin{verbatim} - ok = PyArg_ParseTuple(args, "(ii)s#", &i, &j, &s, &size); - /* A pair of ints and a string, whose size is also returned */ - /* Possible Python call: f((1, 2), 'three') */ -\end{verbatim} - -\begin{verbatim} - { - const char *file; - const char *mode = "r"; - int bufsize = 0; - ok = PyArg_ParseTuple(args, "s|si", &file, &mode, &bufsize); - /* A string, and optionally another string and an integer */ - /* Possible Python calls: - f('spam') - f('spam', 'w') - f('spam', 'wb', 100000) */ - } -\end{verbatim} - -\begin{verbatim} - { - int left, top, right, bottom, h, v; - ok = PyArg_ParseTuple(args, "((ii)(ii))(ii)", - &left, &top, &right, &bottom, &h, &v); - /* A rectangle and a point */ - /* Possible Python call: - f(((0, 0), (400, 300)), (10, 10)) */ - } -\end{verbatim} - -\begin{verbatim} - { - Py_complex c; - ok = PyArg_ParseTuple(args, "D:myfunction", &c); - /* a complex, also providing a function name for errors */ - /* Possible Python call: myfunction(1+2j) */ - } -\end{verbatim} - - -\section{Keyword Parameters for Extension Functions - \label{parseTupleAndKeywords}} - -\ttindex{PyArg_ParseTupleAndKeywords()} - -The \cfunction{PyArg_ParseTupleAndKeywords()} function is declared as -follows: - -\begin{verbatim} -int PyArg_ParseTupleAndKeywords(PyObject *arg, PyObject *kwdict, - char *format, char *kwlist[], ...); -\end{verbatim} - -The \var{arg} and \var{format} parameters are identical to those of the -\cfunction{PyArg_ParseTuple()} function. The \var{kwdict} parameter -is the dictionary of keywords received as the third parameter from the -Python runtime. The \var{kwlist} parameter is a \NULL-terminated -list of strings which identify the parameters; the names are matched -with the type information from \var{format} from left to right. On -success, \cfunction{PyArg_ParseTupleAndKeywords()} returns true, -otherwise it returns false and raises an appropriate exception. - -\note{Nested tuples cannot be parsed when using keyword -arguments! Keyword parameters passed in which are not present in the -\var{kwlist} will cause \exception{TypeError} to be raised.} - -Here is an example module which uses keywords, based on an example by -Geoff Philbrick (\email{philbrick@hks.com}):% -\index{Philbrick, Geoff} - -\begin{verbatim} -#include "Python.h" - -static PyObject * -keywdarg_parrot(PyObject *self, PyObject *args, PyObject *keywds) -{ - int voltage; - char *state = "a stiff"; - char *action = "voom"; - char *type = "Norwegian Blue"; - - static char *kwlist[] = {"voltage", "state", "action", "type", NULL}; - - if (!PyArg_ParseTupleAndKeywords(args, keywds, "i|sss", kwlist, - &voltage, &state, &action, &type)) - return NULL; - - printf("-- This parrot wouldn't %s if you put %i Volts through it.\n", - action, voltage); - printf("-- Lovely plumage, the %s -- It's %s!\n", type, state); - - Py_INCREF(Py_None); - - return Py_None; -} - -static PyMethodDef keywdarg_methods[] = { - /* The cast of the function is necessary since PyCFunction values - * only take two PyObject* parameters, and keywdarg_parrot() takes - * three. - */ - {"parrot", (PyCFunction)keywdarg_parrot, METH_VARARGS | METH_KEYWORDS, - "Print a lovely skit to standard output."}, - {NULL, NULL, 0, NULL} /* sentinel */ -}; -\end{verbatim} - -\begin{verbatim} -void -initkeywdarg(void) -{ - /* Create the module and add the functions */ - Py_InitModule("keywdarg", keywdarg_methods); -} -\end{verbatim} - - -\section{Building Arbitrary Values - \label{buildValue}} - -This function is the counterpart to \cfunction{PyArg_ParseTuple()}. It is -declared as follows: - -\begin{verbatim} -PyObject *Py_BuildValue(char *format, ...); -\end{verbatim} - -It recognizes a set of format units similar to the ones recognized by -\cfunction{PyArg_ParseTuple()}, but the arguments (which are input to the -function, not output) must not be pointers, just values. It returns a -new Python object, suitable for returning from a C function called -from Python. - -One difference with \cfunction{PyArg_ParseTuple()}: while the latter -requires its first argument to be a tuple (since Python argument lists -are always represented as tuples internally), -\cfunction{Py_BuildValue()} does not always build a tuple. It builds -a tuple only if its format string contains two or more format units. -If the format string is empty, it returns \code{None}; if it contains -exactly one format unit, it returns whatever object is described by -that format unit. To force it to return a tuple of size 0 or one, -parenthesize the format string. - -Examples (to the left the call, to the right the resulting Python value): - -\begin{verbatim} - Py_BuildValue("") None - Py_BuildValue("i", 123) 123 - Py_BuildValue("iii", 123, 456, 789) (123, 456, 789) - Py_BuildValue("s", "hello") 'hello' - Py_BuildValue("ss", "hello", "world") ('hello', 'world') - Py_BuildValue("s#", "hello", 4) 'hell' - Py_BuildValue("()") () - Py_BuildValue("(i)", 123) (123,) - Py_BuildValue("(ii)", 123, 456) (123, 456) - Py_BuildValue("(i,i)", 123, 456) (123, 456) - Py_BuildValue("[i,i]", 123, 456) [123, 456] - Py_BuildValue("{s:i,s:i}", - "abc", 123, "def", 456) {'abc': 123, 'def': 456} - Py_BuildValue("((ii)(ii)) (ii)", - 1, 2, 3, 4, 5, 6) (((1, 2), (3, 4)), (5, 6)) -\end{verbatim} - - -\section{Reference Counts - \label{refcounts}} - -In languages like C or \Cpp, the programmer is responsible for -dynamic allocation and deallocation of memory on the heap. In C, -this is done using the functions \cfunction{malloc()} and -\cfunction{free()}. In \Cpp, the operators \keyword{new} and -\keyword{delete} are used with essentially the same meaning and -we'll restrict the following discussion to the C case. - -Every block of memory allocated with \cfunction{malloc()} should -eventually be returned to the pool of available memory by exactly one -call to \cfunction{free()}. It is important to call -\cfunction{free()} at the right time. If a block's address is -forgotten but \cfunction{free()} is not called for it, the memory it -occupies cannot be reused until the program terminates. This is -called a \dfn{memory leak}. On the other hand, if a program calls -\cfunction{free()} for a block and then continues to use the block, it -creates a conflict with re-use of the block through another -\cfunction{malloc()} call. This is called \dfn{using freed memory}. -It has the same bad consequences as referencing uninitialized data --- -core dumps, wrong results, mysterious crashes. - -Common causes of memory leaks are unusual paths through the code. For -instance, a function may allocate a block of memory, do some -calculation, and then free the block again. Now a change in the -requirements for the function may add a test to the calculation that -detects an error condition and can return prematurely from the -function. It's easy to forget to free the allocated memory block when -taking this premature exit, especially when it is added later to the -code. Such leaks, once introduced, often go undetected for a long -time: the error exit is taken only in a small fraction of all calls, -and most modern machines have plenty of virtual memory, so the leak -only becomes apparent in a long-running process that uses the leaking -function frequently. Therefore, it's important to prevent leaks from -happening by having a coding convention or strategy that minimizes -this kind of errors. - -Since Python makes heavy use of \cfunction{malloc()} and -\cfunction{free()}, it needs a strategy to avoid memory leaks as well -as the use of freed memory. The chosen method is called -\dfn{reference counting}. The principle is simple: every object -contains a counter, which is incremented when a reference to the -object is stored somewhere, and which is decremented when a reference -to it is deleted. When the counter reaches zero, the last reference -to the object has been deleted and the object is freed. - -An alternative strategy is called \dfn{automatic garbage collection}. -(Sometimes, reference counting is also referred to as a garbage -collection strategy, hence my use of ``automatic'' to distinguish the -two.) The big advantage of automatic garbage collection is that the -user doesn't need to call \cfunction{free()} explicitly. (Another claimed -advantage is an improvement in speed or memory usage --- this is no -hard fact however.) The disadvantage is that for C, there is no -truly portable automatic garbage collector, while reference counting -can be implemented portably (as long as the functions \cfunction{malloc()} -and \cfunction{free()} are available --- which the C Standard guarantees). -Maybe some day a sufficiently portable automatic garbage collector -will be available for C. Until then, we'll have to live with -reference counts. - -While Python uses the traditional reference counting implementation, -it also offers a cycle detector that works to detect reference -cycles. This allows applications to not worry about creating direct -or indirect circular references; these are the weakness of garbage -collection implemented using only reference counting. Reference -cycles consist of objects which contain (possibly indirect) references -to themselves, so that each object in the cycle has a reference count -which is non-zero. Typical reference counting implementations are not -able to reclaim the memory belonging to any objects in a reference -cycle, or referenced from the objects in the cycle, even though there -are no further references to the cycle itself. - -The cycle detector is able to detect garbage cycles and can reclaim -them so long as there are no finalizers implemented in Python -(\method{__del__()} methods). When there are such finalizers, the -detector exposes the cycles through the \ulink{\module{gc} -module}{../lib/module-gc.html} (specifically, the \code{garbage} -variable in that module). The \module{gc} module also exposes a way -to run the detector (the \function{collect()} function), as well as -configuration interfaces and the ability to disable the detector at -runtime. The cycle detector is considered an optional component; -though it is included by default, it can be disabled at build time -using the \longprogramopt{without-cycle-gc} option to the -\program{configure} script on \UNIX{} platforms (including Mac OS X) -or by removing the definition of \code{WITH_CYCLE_GC} in the -\file{pyconfig.h} header on other platforms. If the cycle detector is -disabled in this way, the \module{gc} module will not be available. - - -\subsection{Reference Counting in Python - \label{refcountsInPython}} - -There are two macros, \code{Py_INCREF(x)} and \code{Py_DECREF(x)}, -which handle the incrementing and decrementing of the reference count. -\cfunction{Py_DECREF()} also frees the object when the count reaches zero. -For flexibility, it doesn't call \cfunction{free()} directly --- rather, it -makes a call through a function pointer in the object's \dfn{type -object}. For this purpose (and others), every object also contains a -pointer to its type object. - -The big question now remains: when to use \code{Py_INCREF(x)} and -\code{Py_DECREF(x)}? Let's first introduce some terms. Nobody -``owns'' an object; however, you can \dfn{own a reference} to an -object. An object's reference count is now defined as the number of -owned references to it. The owner of a reference is responsible for -calling \cfunction{Py_DECREF()} when the reference is no longer -needed. Ownership of a reference can be transferred. There are three -ways to dispose of an owned reference: pass it on, store it, or call -\cfunction{Py_DECREF()}. Forgetting to dispose of an owned reference -creates a memory leak. - -It is also possible to \dfn{borrow}\footnote{The metaphor of -``borrowing'' a reference is not completely correct: the owner still -has a copy of the reference.} a reference to an object. The borrower -of a reference should not call \cfunction{Py_DECREF()}. The borrower must -not hold on to the object longer than the owner from which it was -borrowed. Using a borrowed reference after the owner has disposed of -it risks using freed memory and should be avoided -completely.\footnote{Checking that the reference count is at least 1 -\strong{does not work} --- the reference count itself could be in -freed memory and may thus be reused for another object!} - -The advantage of borrowing over owning a reference is that you don't -need to take care of disposing of the reference on all possible paths -through the code --- in other words, with a borrowed reference you -don't run the risk of leaking when a premature exit is taken. The -disadvantage of borrowing over leaking is that there are some subtle -situations where in seemingly correct code a borrowed reference can be -used after the owner from which it was borrowed has in fact disposed -of it. - -A borrowed reference can be changed into an owned reference by calling -\cfunction{Py_INCREF()}. This does not affect the status of the owner from -which the reference was borrowed --- it creates a new owned reference, -and gives full owner responsibilities (the new owner must -dispose of the reference properly, as well as the previous owner). - - -\subsection{Ownership Rules - \label{ownershipRules}} - -Whenever an object reference is passed into or out of a function, it -is part of the function's interface specification whether ownership is -transferred with the reference or not. - -Most functions that return a reference to an object pass on ownership -with the reference. In particular, all functions whose function it is -to create a new object, such as \cfunction{PyInt_FromLong()} and -\cfunction{Py_BuildValue()}, pass ownership to the receiver. Even if -the object is not actually new, you still receive ownership of a new -reference to that object. For instance, \cfunction{PyInt_FromLong()} -maintains a cache of popular values and can return a reference to a -cached item. - -Many functions that extract objects from other objects also transfer -ownership with the reference, for instance -\cfunction{PyObject_GetAttrString()}. The picture is less clear, here, -however, since a few common routines are exceptions: -\cfunction{PyTuple_GetItem()}, \cfunction{PyList_GetItem()}, -\cfunction{PyDict_GetItem()}, and \cfunction{PyDict_GetItemString()} -all return references that you borrow from the tuple, list or -dictionary. - -The function \cfunction{PyImport_AddModule()} also returns a borrowed -reference, even though it may actually create the object it returns: -this is possible because an owned reference to the object is stored in -\code{sys.modules}. - -When you pass an object reference into another function, in general, -the function borrows the reference from you --- if it needs to store -it, it will use \cfunction{Py_INCREF()} to become an independent -owner. There are exactly two important exceptions to this rule: -\cfunction{PyTuple_SetItem()} and \cfunction{PyList_SetItem()}. These -functions take over ownership of the item passed to them --- even if -they fail! (Note that \cfunction{PyDict_SetItem()} and friends don't -take over ownership --- they are ``normal.'') - -When a C function is called from Python, it borrows references to its -arguments from the caller. The caller owns a reference to the object, -so the borrowed reference's lifetime is guaranteed until the function -returns. Only when such a borrowed reference must be stored or passed -on, it must be turned into an owned reference by calling -\cfunction{Py_INCREF()}. - -The object reference returned from a C function that is called from -Python must be an owned reference --- ownership is transferred from -the function to its caller. - - -\subsection{Thin Ice - \label{thinIce}} - -There are a few situations where seemingly harmless use of a borrowed -reference can lead to problems. These all have to do with implicit -invocations of the interpreter, which can cause the owner of a -reference to dispose of it. - -The first and most important case to know about is using -\cfunction{Py_DECREF()} on an unrelated object while borrowing a -reference to a list item. For instance: - -\begin{verbatim} -void -bug(PyObject *list) -{ - PyObject *item = PyList_GetItem(list, 0); - - PyList_SetItem(list, 1, PyInt_FromLong(0L)); - PyObject_Print(item, stdout, 0); /* BUG! */ -} -\end{verbatim} - -This function first borrows a reference to \code{list[0]}, then -replaces \code{list[1]} with the value \code{0}, and finally prints -the borrowed reference. Looks harmless, right? But it's not! - -Let's follow the control flow into \cfunction{PyList_SetItem()}. The list -owns references to all its items, so when item 1 is replaced, it has -to dispose of the original item 1. Now let's suppose the original -item 1 was an instance of a user-defined class, and let's further -suppose that the class defined a \method{__del__()} method. If this -class instance has a reference count of 1, disposing of it will call -its \method{__del__()} method. - -Since it is written in Python, the \method{__del__()} method can execute -arbitrary Python code. Could it perhaps do something to invalidate -the reference to \code{item} in \cfunction{bug()}? You bet! Assuming -that the list passed into \cfunction{bug()} is accessible to the -\method{__del__()} method, it could execute a statement to the effect of -\samp{del list[0]}, and assuming this was the last reference to that -object, it would free the memory associated with it, thereby -invalidating \code{item}. - -The solution, once you know the source of the problem, is easy: -temporarily increment the reference count. The correct version of the -function reads: - -\begin{verbatim} -void -no_bug(PyObject *list) -{ - PyObject *item = PyList_GetItem(list, 0); - - Py_INCREF(item); - PyList_SetItem(list, 1, PyInt_FromLong(0L)); - PyObject_Print(item, stdout, 0); - Py_DECREF(item); -} -\end{verbatim} - -This is a true story. An older version of Python contained variants -of this bug and someone spent a considerable amount of time in a C -debugger to figure out why his \method{__del__()} methods would fail... - -The second case of problems with a borrowed reference is a variant -involving threads. Normally, multiple threads in the Python -interpreter can't get in each other's way, because there is a global -lock protecting Python's entire object space. However, it is possible -to temporarily release this lock using the macro -\csimplemacro{Py_BEGIN_ALLOW_THREADS}, and to re-acquire it using -\csimplemacro{Py_END_ALLOW_THREADS}. This is common around blocking -I/O calls, to let other threads use the processor while waiting for -the I/O to complete. Obviously, the following function has the same -problem as the previous one: - -\begin{verbatim} -void -bug(PyObject *list) -{ - PyObject *item = PyList_GetItem(list, 0); - Py_BEGIN_ALLOW_THREADS - ...some blocking I/O call... - Py_END_ALLOW_THREADS - PyObject_Print(item, stdout, 0); /* BUG! */ -} -\end{verbatim} - - -\subsection{NULL Pointers - \label{nullPointers}} - -In general, functions that take object references as arguments do not -expect you to pass them \NULL{} pointers, and will dump core (or -cause later core dumps) if you do so. Functions that return object -references generally return \NULL{} only to indicate that an -exception occurred. The reason for not testing for \NULL{} -arguments is that functions often pass the objects they receive on to -other function --- if each function were to test for \NULL, -there would be a lot of redundant tests and the code would run more -slowly. - -It is better to test for \NULL{} only at the ``source:'' when a -pointer that may be \NULL{} is received, for example, from -\cfunction{malloc()} or from a function that may raise an exception. - -The macros \cfunction{Py_INCREF()} and \cfunction{Py_DECREF()} -do not check for \NULL{} pointers --- however, their variants -\cfunction{Py_XINCREF()} and \cfunction{Py_XDECREF()} do. - -The macros for checking for a particular object type -(\code{Py\var{type}_Check()}) don't check for \NULL{} pointers --- -again, there is much code that calls several of these in a row to test -an object against various different expected types, and this would -generate redundant tests. There are no variants with \NULL{} -checking. - -The C function calling mechanism guarantees that the argument list -passed to C functions (\code{args} in the examples) is never -\NULL{} --- in fact it guarantees that it is always a tuple.\footnote{ -These guarantees don't hold when you use the ``old'' style -calling convention --- this is still found in much existing code.} - -It is a severe error to ever let a \NULL{} pointer ``escape'' to -the Python user. - -% Frank Stajano: -% A pedagogically buggy example, along the lines of the previous listing, -% would be helpful here -- showing in more concrete terms what sort of -% actions could cause the problem. I can't very well imagine it from the -% description. - - -\section{Writing Extensions in \Cpp - \label{cplusplus}} - -It is possible to write extension modules in \Cpp. Some restrictions -apply. If the main program (the Python interpreter) is compiled and -linked by the C compiler, global or static objects with constructors -cannot be used. This is not a problem if the main program is linked -by the \Cpp{} compiler. Functions that will be called by the -Python interpreter (in particular, module initialization functions) -have to be declared using \code{extern "C"}. -It is unnecessary to enclose the Python header files in -\code{extern "C" \{...\}} --- they use this form already if the symbol -\samp{__cplusplus} is defined (all recent \Cpp{} compilers define this -symbol). - - -\section{Providing a C API for an Extension Module - \label{using-cobjects}} -\sectionauthor{Konrad Hinsen}{hinsen@cnrs-orleans.fr} - -Many extension modules just provide new functions and types to be -used from Python, but sometimes the code in an extension module can -be useful for other extension modules. For example, an extension -module could implement a type ``collection'' which works like lists -without order. Just like the standard Python list type has a C API -which permits extension modules to create and manipulate lists, this -new collection type should have a set of C functions for direct -manipulation from other extension modules. - -At first sight this seems easy: just write the functions (without -declaring them \keyword{static}, of course), provide an appropriate -header file, and document the C API. And in fact this would work if -all extension modules were always linked statically with the Python -interpreter. When modules are used as shared libraries, however, the -symbols defined in one module may not be visible to another module. -The details of visibility depend on the operating system; some systems -use one global namespace for the Python interpreter and all extension -modules (Windows, for example), whereas others require an explicit -list of imported symbols at module link time (AIX is one example), or -offer a choice of different strategies (most Unices). And even if -symbols are globally visible, the module whose functions one wishes to -call might not have been loaded yet! - -Portability therefore requires not to make any assumptions about -symbol visibility. This means that all symbols in extension modules -should be declared \keyword{static}, except for the module's -initialization function, in order to avoid name clashes with other -extension modules (as discussed in section~\ref{methodTable}). And it -means that symbols that \emph{should} be accessible from other -extension modules must be exported in a different way. - -Python provides a special mechanism to pass C-level information -(pointers) from one extension module to another one: CObjects. -A CObject is a Python data type which stores a pointer (\ctype{void -*}). CObjects can only be created and accessed via their C API, but -they can be passed around like any other Python object. In particular, -they can be assigned to a name in an extension module's namespace. -Other extension modules can then import this module, retrieve the -value of this name, and then retrieve the pointer from the CObject. - -There are many ways in which CObjects can be used to export the C API -of an extension module. Each name could get its own CObject, or all C -API pointers could be stored in an array whose address is published in -a CObject. And the various tasks of storing and retrieving the pointers -can be distributed in different ways between the module providing the -code and the client modules. - -The following example demonstrates an approach that puts most of the -burden on the writer of the exporting module, which is appropriate -for commonly used library modules. It stores all C API pointers -(just one in the example!) in an array of \ctype{void} pointers which -becomes the value of a CObject. The header file corresponding to -the module provides a macro that takes care of importing the module -and retrieving its C API pointers; client modules only have to call -this macro before accessing the C API. - -The exporting module is a modification of the \module{spam} module from -section~\ref{simpleExample}. The function \function{spam.system()} -does not call the C library function \cfunction{system()} directly, -but a function \cfunction{PySpam_System()}, which would of course do -something more complicated in reality (such as adding ``spam'' to -every command). This function \cfunction{PySpam_System()} is also -exported to other extension modules. - -The function \cfunction{PySpam_System()} is a plain C function, -declared \keyword{static} like everything else: - -\begin{verbatim} -static int -PySpam_System(const char *command) -{ - return system(command); -} -\end{verbatim} - -The function \cfunction{spam_system()} is modified in a trivial way: - -\begin{verbatim} -static PyObject * -spam_system(PyObject *self, PyObject *args) -{ - const char *command; - int sts; - - if (!PyArg_ParseTuple(args, "s", &command)) - return NULL; - sts = PySpam_System(command); - return Py_BuildValue("i", sts); -} -\end{verbatim} - -In the beginning of the module, right after the line - -\begin{verbatim} -#include "Python.h" -\end{verbatim} - -two more lines must be added: - -\begin{verbatim} -#define SPAM_MODULE -#include "spammodule.h" -\end{verbatim} - -The \code{\#define} is used to tell the header file that it is being -included in the exporting module, not a client module. Finally, -the module's initialization function must take care of initializing -the C API pointer array: - -\begin{verbatim} -PyMODINIT_FUNC -initspam(void) -{ - PyObject *m; - static void *PySpam_API[PySpam_API_pointers]; - PyObject *c_api_object; - - m = Py_InitModule("spam", SpamMethods); - if (m == NULL) - return; - - /* Initialize the C API pointer array */ - PySpam_API[PySpam_System_NUM] = (void *)PySpam_System; - - /* Create a CObject containing the API pointer array's address */ - c_api_object = PyCObject_FromVoidPtr((void *)PySpam_API, NULL); - - if (c_api_object != NULL) - PyModule_AddObject(m, "_C_API", c_api_object); -} -\end{verbatim} - -Note that \code{PySpam_API} is declared \keyword{static}; otherwise -the pointer array would disappear when \function{initspam()} terminates! - -The bulk of the work is in the header file \file{spammodule.h}, -which looks like this: - -\begin{verbatim} -#ifndef Py_SPAMMODULE_H -#define Py_SPAMMODULE_H -#ifdef __cplusplus -extern "C" { -#endif - -/* Header file for spammodule */ - -/* C API functions */ -#define PySpam_System_NUM 0 -#define PySpam_System_RETURN int -#define PySpam_System_PROTO (const char *command) - -/* Total number of C API pointers */ -#define PySpam_API_pointers 1 - - -#ifdef SPAM_MODULE -/* This section is used when compiling spammodule.c */ - -static PySpam_System_RETURN PySpam_System PySpam_System_PROTO; - -#else -/* This section is used in modules that use spammodule's API */ - -static void **PySpam_API; - -#define PySpam_System \ - (*(PySpam_System_RETURN (*)PySpam_System_PROTO) PySpam_API[PySpam_System_NUM]) - -/* Return -1 and set exception on error, 0 on success. */ -static int -import_spam(void) -{ - PyObject *module = PyImport_ImportModule("spam"); - - if (module != NULL) { - PyObject *c_api_object = PyObject_GetAttrString(module, "_C_API"); - if (c_api_object == NULL) - return -1; - if (PyCObject_Check(c_api_object)) - PySpam_API = (void **)PyCObject_AsVoidPtr(c_api_object); - Py_DECREF(c_api_object); - } - return 0; -} - -#endif - -#ifdef __cplusplus -} -#endif - -#endif /* !defined(Py_SPAMMODULE_H) */ -\end{verbatim} - -All that a client module must do in order to have access to the -function \cfunction{PySpam_System()} is to call the function (or -rather macro) \cfunction{import_spam()} in its initialization -function: - -\begin{verbatim} -PyMODINIT_FUNC -initclient(void) -{ - PyObject *m; - - m = Py_InitModule("client", ClientMethods); - if (m == NULL) - return; - if (import_spam() < 0) - return; - /* additional initialization can happen here */ -} -\end{verbatim} - -The main disadvantage of this approach is that the file -\file{spammodule.h} is rather complicated. However, the -basic structure is the same for each function that is -exported, so it has to be learned only once. - -Finally it should be mentioned that CObjects offer additional -functionality, which is especially useful for memory allocation and -deallocation of the pointer stored in a CObject. The details -are described in the \citetitle[../api/api.html]{Python/C API -Reference Manual} in the section -``\ulink{CObjects}{../api/cObjects.html}'' and in the implementation -of CObjects (files \file{Include/cobject.h} and -\file{Objects/cobject.c} in the Python source code distribution). diff --git a/Doc/ext/newtypes.tex b/Doc/ext/newtypes.tex deleted file mode 100644 index 5c1f0ae..0000000 --- a/Doc/ext/newtypes.tex +++ /dev/null @@ -1,1765 +0,0 @@ -\chapter{Defining New Types - \label{defining-new-types}} -\sectionauthor{Michael Hudson}{mwh@python.net} -\sectionauthor{Dave Kuhlman}{dkuhlman@rexx.com} -\sectionauthor{Jim Fulton}{jim@zope.com} - -As mentioned in the last chapter, Python allows the writer of an -extension module to define new types that can be manipulated from -Python code, much like strings and lists in core Python. - -This is not hard; the code for all extension types follows a pattern, -but there are some details that you need to understand before you can -get started. - -\begin{notice} -The way new types are defined changed dramatically (and for the -better) in Python 2.2. This document documents how to define new -types for Python 2.2 and later. If you need to support older -versions of Python, you will need to refer to -\ulink{older versions of this documentation} - {http://www.python.org/doc/versions/}. -\end{notice} - -\section{The Basics - \label{dnt-basics}} - -The Python runtime sees all Python objects as variables of type -\ctype{PyObject*}. A \ctype{PyObject} is not a very magnificent -object - it just contains the refcount and a pointer to the object's -``type object''. This is where the action is; the type object -determines which (C) functions get called when, for instance, an -attribute gets looked up on an object or it is multiplied by another -object. These C functions are called ``type methods'' to distinguish -them from things like \code{[].append} (which we call ``object -methods''). - -So, if you want to define a new object type, you need to create a new -type object. - -This sort of thing can only be explained by example, so here's a -minimal, but complete, module that defines a new type: - -\verbatiminput{noddy.c} - -Now that's quite a bit to take in at once, but hopefully bits will -seem familiar from the last chapter. - -The first bit that will be new is: - -\begin{verbatim} -typedef struct { - PyObject_HEAD -} noddy_NoddyObject; -\end{verbatim} - -This is what a Noddy object will contain---in this case, nothing more -than every Python object contains, namely a refcount and a pointer to a type -object. These are the fields the \code{PyObject_HEAD} macro brings -in. The reason for the macro is to standardize the layout and to -enable special debugging fields in debug builds. Note that there is -no semicolon after the \code{PyObject_HEAD} macro; one is included in -the macro definition. Be wary of adding one by accident; it's easy to -do from habit, and your compiler might not complain, but someone -else's probably will! (On Windows, MSVC is known to call this an -error and refuse to compile the code.) - -For contrast, let's take a look at the corresponding definition for -standard Python integers: - -\begin{verbatim} -typedef struct { - PyObject_HEAD - long ob_ival; -} PyIntObject; -\end{verbatim} - -Moving on, we come to the crunch --- the type object. - -\begin{verbatim} -static PyTypeObject noddy_NoddyType = { - PyObject_HEAD_INIT(NULL) - 0, /*ob_size*/ - "noddy.Noddy", /*tp_name*/ - sizeof(noddy_NoddyObject), /*tp_basicsize*/ - 0, /*tp_itemsize*/ - 0, /*tp_dealloc*/ - 0, /*tp_print*/ - 0, /*tp_getattr*/ - 0, /*tp_setattr*/ - 0, /*tp_compare*/ - 0, /*tp_repr*/ - 0, /*tp_as_number*/ - 0, /*tp_as_sequence*/ - 0, /*tp_as_mapping*/ - 0, /*tp_hash */ - 0, /*tp_call*/ - 0, /*tp_str*/ - 0, /*tp_getattro*/ - 0, /*tp_setattro*/ - 0, /*tp_as_buffer*/ - Py_TPFLAGS_DEFAULT, /*tp_flags*/ - "Noddy objects", /* tp_doc */ -}; -\end{verbatim} - -Now if you go and look up the definition of \ctype{PyTypeObject} in -\file{object.h} you'll see that it has many more fields that the -definition above. The remaining fields will be filled with zeros by -the C compiler, and it's common practice to not specify them -explicitly unless you need them. - -This is so important that we're going to pick the top of it apart still -further: - -\begin{verbatim} - PyObject_HEAD_INIT(NULL) -\end{verbatim} - -This line is a bit of a wart; what we'd like to write is: - -\begin{verbatim} - PyObject_HEAD_INIT(&PyType_Type) -\end{verbatim} - -as the type of a type object is ``type'', but this isn't strictly -conforming C and some compilers complain. Fortunately, this member -will be filled in for us by \cfunction{PyType_Ready()}. - -\begin{verbatim} - 0, /* ob_size */ -\end{verbatim} - -The \member{ob_size} field of the header is not used; its presence in -the type structure is a historical artifact that is maintained for -binary compatibility with extension modules compiled for older -versions of Python. Always set this field to zero. - -\begin{verbatim} - "noddy.Noddy", /* tp_name */ -\end{verbatim} - -The name of our type. This will appear in the default textual -representation of our objects and in some error messages, for example: - -\begin{verbatim} ->>> "" + noddy.new_noddy() -Traceback (most recent call last): - File "<stdin>", line 1, in ? -TypeError: cannot add type "noddy.Noddy" to string -\end{verbatim} - -Note that the name is a dotted name that includes both the module name -and the name of the type within the module. The module in this case is -\module{noddy} and the type is \class{Noddy}, so we set the type name -to \class{noddy.Noddy}. - -\begin{verbatim} - sizeof(noddy_NoddyObject), /* tp_basicsize */ -\end{verbatim} - -This is so that Python knows how much memory to allocate when you call -\cfunction{PyObject_New()}. - -\note{If you want your type to be subclassable from Python, and your -type has the same \member{tp_basicsize} as its base type, you may -have problems with multiple inheritance. A Python subclass of your -type will have to list your type first in its \member{__bases__}, or -else it will not be able to call your type's \method{__new__} method -without getting an error. You can avoid this problem by ensuring -that your type has a larger value for \member{tp_basicsize} than -its base type does. Most of the time, this will be true anyway, -because either your base type will be \class{object}, or else you will -be adding data members to your base type, and therefore increasing its -size.} - -\begin{verbatim} - 0, /* tp_itemsize */ -\end{verbatim} - -This has to do with variable length objects like lists and strings. -Ignore this for now. - -Skipping a number of type methods that we don't provide, we set the -class flags to \constant{Py_TPFLAGS_DEFAULT}. - -\begin{verbatim} - Py_TPFLAGS_DEFAULT, /*tp_flags*/ -\end{verbatim} - -All types should include this constant in their flags. It enables all -of the members defined by the current version of Python. - -We provide a doc string for the type in \member{tp_doc}. - -\begin{verbatim} - "Noddy objects", /* tp_doc */ -\end{verbatim} - -Now we get into the type methods, the things that make your objects -different from the others. We aren't going to implement any of these -in this version of the module. We'll expand this example later to -have more interesting behavior. - -For now, all we want to be able to do is to create new \class{Noddy} -objects. To enable object creation, we have to provide a -\member{tp_new} implementation. In this case, we can just use the -default implementation provided by the API function -\cfunction{PyType_GenericNew()}. We'd like to just assign this to the -\member{tp_new} slot, but we can't, for portability sake, On some -platforms or compilers, we can't statically initialize a structure -member with a function defined in another C module, so, instead, we'll -assign the \member{tp_new} slot in the module initialization function -just before calling \cfunction{PyType_Ready()}: - -\begin{verbatim} - noddy_NoddyType.tp_new = PyType_GenericNew; - if (PyType_Ready(&noddy_NoddyType) < 0) - return; -\end{verbatim} - -All the other type methods are \NULL, so we'll go over them later ---- that's for a later section! - -Everything else in the file should be familiar, except for some code -in \cfunction{initnoddy()}: - -\begin{verbatim} - if (PyType_Ready(&noddy_NoddyType) < 0) - return; -\end{verbatim} - -This initializes the \class{Noddy} type, filing in a number of -members, including \member{ob_type} that we initially set to \NULL. - -\begin{verbatim} - PyModule_AddObject(m, "Noddy", (PyObject *)&noddy_NoddyType); -\end{verbatim} - -This adds the type to the module dictionary. This allows us to create -\class{Noddy} instances by calling the \class{Noddy} class: - -\begin{verbatim} ->>> import noddy ->>> mynoddy = noddy.Noddy() -\end{verbatim} - -That's it! All that remains is to build it; put the above code in a -file called \file{noddy.c} and - -\begin{verbatim} -from distutils.core import setup, Extension -setup(name="noddy", version="1.0", - ext_modules=[Extension("noddy", ["noddy.c"])]) -\end{verbatim} - -in a file called \file{setup.py}; then typing - -\begin{verbatim} -$ python setup.py build -\end{verbatim} %$ <-- bow to font-lock ;-( - -at a shell should produce a file \file{noddy.so} in a subdirectory; -move to that directory and fire up Python --- you should be able to -\code{import noddy} and play around with Noddy objects. - -That wasn't so hard, was it? - -Of course, the current Noddy type is pretty uninteresting. It has no -data and doesn't do anything. It can't even be subclassed. - -\subsection{Adding data and methods to the Basic example} - -Let's expend the basic example to add some data and methods. Let's -also make the type usable as a base class. We'll create -a new module, \module{noddy2} that adds these capabilities: - -\verbatiminput{noddy2.c} - -This version of the module has a number of changes. - -We've added an extra include: - -\begin{verbatim} -#include "structmember.h" -\end{verbatim} - -This include provides declarations that we use to handle attributes, -as described a bit later. - -The name of the \class{Noddy} object structure has been shortened to -\class{Noddy}. The type object name has been shortened to -\class{NoddyType}. - -The \class{Noddy} type now has three data attributes, \var{first}, -\var{last}, and \var{number}. The \var{first} and \var{last} -variables are Python strings containing first and last names. The -\var{number} attribute is an integer. - -The object structure is updated accordingly: - -\begin{verbatim} -typedef struct { - PyObject_HEAD - PyObject *first; - PyObject *last; - int number; -} Noddy; -\end{verbatim} - -Because we now have data to manage, we have to be more careful about -object allocation and deallocation. At a minimum, we need a -deallocation method: - -\begin{verbatim} -static void -Noddy_dealloc(Noddy* self) -{ - Py_XDECREF(self->first); - Py_XDECREF(self->last); - self->ob_type->tp_free((PyObject*)self); -} -\end{verbatim} - -which is assigned to the \member{tp_dealloc} member: - -\begin{verbatim} - (destructor)Noddy_dealloc, /*tp_dealloc*/ -\end{verbatim} - -This method decrements the reference counts of the two Python -attributes. We use \cfunction{Py_XDECREF()} here because the -\member{first} and \member{last} members could be \NULL. It then -calls the \member{tp_free} member of the object's type to free the -object's memory. Note that the object's type might not be -\class{NoddyType}, because the object may be an instance of a -subclass. - -We want to make sure that the first and last names are initialized to -empty strings, so we provide a new method: - -\begin{verbatim} -static PyObject * -Noddy_new(PyTypeObject *type, PyObject *args, PyObject *kwds) -{ - Noddy *self; - - self = (Noddy *)type->tp_alloc(type, 0); - if (self != NULL) { - self->first = PyString_FromString(""); - if (self->first == NULL) - { - Py_DECREF(self); - return NULL; - } - - self->last = PyString_FromString(""); - if (self->last == NULL) - { - Py_DECREF(self); - return NULL; - } - - self->number = 0; - } - - return (PyObject *)self; -} -\end{verbatim} - -and install it in the \member{tp_new} member: - -\begin{verbatim} - Noddy_new, /* tp_new */ -\end{verbatim} - -The new member is responsible for creating (as opposed to -initializing) objects of the type. It is exposed in Python as the -\method{__new__()} method. See the paper titled ``Unifying types and -classes in Python'' for a detailed discussion of the \method{__new__()} -method. One reason to implement a new method is to assure the initial -values of instance variables. In this case, we use the new method to -make sure that the initial values of the members \member{first} and -\member{last} are not \NULL. If we didn't care whether the initial -values were \NULL, we could have used \cfunction{PyType_GenericNew()} as -our new method, as we did before. \cfunction{PyType_GenericNew()} -initializes all of the instance variable members to \NULL. - -The new method is a static method that is passed the type being -instantiated and any arguments passed when the type was called, -and that returns the new object created. New methods always accept -positional and keyword arguments, but they often ignore the arguments, -leaving the argument handling to initializer methods. Note that if the -type supports subclassing, the type passed may not be the type being -defined. The new method calls the tp_alloc slot to allocate memory. -We don't fill the \member{tp_alloc} slot ourselves. Rather -\cfunction{PyType_Ready()} fills it for us by inheriting it from our -base class, which is \class{object} by default. Most types use the -default allocation. - -\note{If you are creating a co-operative \member{tp_new} (one that -calls a base type's \member{tp_new} or \method{__new__}), you -must \emph{not} try to determine what method to call using -method resolution order at runtime. Always statically determine -what type you are going to call, and call its \member{tp_new} -directly, or via \code{type->tp_base->tp_new}. If you do -not do this, Python subclasses of your type that also inherit -from other Python-defined classes may not work correctly. -(Specifically, you may not be able to create instances of -such subclasses without getting a \exception{TypeError}.)} - -We provide an initialization function: - -\begin{verbatim} -static int -Noddy_init(Noddy *self, PyObject *args, PyObject *kwds) -{ - PyObject *first=NULL, *last=NULL, *tmp; - - static char *kwlist[] = {"first", "last", "number", NULL}; - - if (! PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist, - &first, &last, - &self->number)) - return -1; - - if (first) { - tmp = self->first; - Py_INCREF(first); - self->first = first; - Py_XDECREF(tmp); - } - - if (last) { - tmp = self->last; - Py_INCREF(last); - self->last = last; - Py_XDECREF(tmp); - } - - return 0; -} -\end{verbatim} - -by filling the \member{tp_init} slot. - -\begin{verbatim} - (initproc)Noddy_init, /* tp_init */ -\end{verbatim} - -The \member{tp_init} slot is exposed in Python as the -\method{__init__()} method. It is used to initialize an object after -it's created. Unlike the new method, we can't guarantee that the -initializer is called. The initializer isn't called when unpickling -objects and it can be overridden. Our initializer accepts arguments -to provide initial values for our instance. Initializers always accept -positional and keyword arguments. - -Initializers can be called multiple times. Anyone can call the -\method{__init__()} method on our objects. For this reason, we have -to be extra careful when assigning the new values. We might be -tempted, for example to assign the \member{first} member like this: - -\begin{verbatim} - if (first) { - Py_XDECREF(self->first); - Py_INCREF(first); - self->first = first; - } -\end{verbatim} - -But this would be risky. Our type doesn't restrict the type of the -\member{first} member, so it could be any kind of object. It could -have a destructor that causes code to be executed that tries to -access the \member{first} member. To be paranoid and protect -ourselves against this possibility, we almost always reassign members -before decrementing their reference counts. When don't we have to do -this? -\begin{itemize} -\item when we absolutely know that the reference count is greater than - 1 -\item when we know that deallocation of the object\footnote{This is - true when we know that the object is a basic type, like a string or - a float.} will not cause any - calls back into our type's code -\item when decrementing a reference count in a \member{tp_dealloc} - handler when garbage-collections is not supported\footnote{We relied - on this in the \member{tp_dealloc} handler in this example, because - our type doesn't support garbage collection. Even if a type supports - garbage collection, there are calls that can be made to ``untrack'' - the object from garbage collection, however, these calls are - advanced and not covered here.} -\end{itemize} - - -We want to want to expose our instance variables as attributes. There -are a number of ways to do that. The simplest way is to define member -definitions: - -\begin{verbatim} -static PyMemberDef Noddy_members[] = { - {"first", T_OBJECT_EX, offsetof(Noddy, first), 0, - "first name"}, - {"last", T_OBJECT_EX, offsetof(Noddy, last), 0, - "last name"}, - {"number", T_INT, offsetof(Noddy, number), 0, - "noddy number"}, - {NULL} /* Sentinel */ -}; -\end{verbatim} - -and put the definitions in the \member{tp_members} slot: - -\begin{verbatim} - Noddy_members, /* tp_members */ -\end{verbatim} - -Each member definition has a member name, type, offset, access flags -and documentation string. See the ``Generic Attribute Management'' -section below for details. - -A disadvantage of this approach is that it doesn't provide a way to -restrict the types of objects that can be assigned to the Python -attributes. We expect the first and last names to be strings, but any -Python objects can be assigned. Further, the attributes can be -deleted, setting the C pointers to \NULL. Even though we can make -sure the members are initialized to non-\NULL{} values, the members can -be set to \NULL{} if the attributes are deleted. - -We define a single method, \method{name}, that outputs the objects -name as the concatenation of the first and last names. - -\begin{verbatim} -static PyObject * -Noddy_name(Noddy* self) -{ - static PyObject *format = NULL; - PyObject *args, *result; - - if (format == NULL) { - format = PyString_FromString("%s %s"); - if (format == NULL) - return NULL; - } - - if (self->first == NULL) { - PyErr_SetString(PyExc_AttributeError, "first"); - return NULL; - } - - if (self->last == NULL) { - PyErr_SetString(PyExc_AttributeError, "last"); - return NULL; - } - - args = Py_BuildValue("OO", self->first, self->last); - if (args == NULL) - return NULL; - - result = PyString_Format(format, args); - Py_DECREF(args); - - return result; -} -\end{verbatim} - -The method is implemented as a C function that takes a \class{Noddy} (or -\class{Noddy} subclass) instance as the first argument. Methods -always take an instance as the first argument. Methods often take -positional and keyword arguments as well, but in this cased we don't -take any and don't need to accept a positional argument tuple or -keyword argument dictionary. This method is equivalent to the Python -method: - -\begin{verbatim} - def name(self): - return "%s %s" % (self.first, self.last) -\end{verbatim} - -Note that we have to check for the possibility that our \member{first} -and \member{last} members are \NULL. This is because they can be -deleted, in which case they are set to \NULL. It would be better to -prevent deletion of these attributes and to restrict the attribute -values to be strings. We'll see how to do that in the next section. - -Now that we've defined the method, we need to create an array of -method definitions: - -\begin{verbatim} -static PyMethodDef Noddy_methods[] = { - {"name", (PyCFunction)Noddy_name, METH_NOARGS, - "Return the name, combining the first and last name" - }, - {NULL} /* Sentinel */ -}; -\end{verbatim} - -and assign them to the \member{tp_methods} slot: - -\begin{verbatim} - Noddy_methods, /* tp_methods */ -\end{verbatim} - -Note that we used the \constant{METH_NOARGS} flag to indicate that the -method is passed no arguments. - -Finally, we'll make our type usable as a base class. We've written -our methods carefully so far so that they don't make any assumptions -about the type of the object being created or used, so all we need to -do is to add the \constant{Py_TPFLAGS_BASETYPE} to our class flag -definition: - -\begin{verbatim} - Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/ -\end{verbatim} - -We rename \cfunction{initnoddy()} to \cfunction{initnoddy2()} -and update the module name passed to \cfunction{Py_InitModule3()}. - -Finally, we update our \file{setup.py} file to build the new module: - -\begin{verbatim} -from distutils.core import setup, Extension -setup(name="noddy", version="1.0", - ext_modules=[ - Extension("noddy", ["noddy.c"]), - Extension("noddy2", ["noddy2.c"]), - ]) -\end{verbatim} - -\subsection{Providing finer control over data attributes} - -In this section, we'll provide finer control over how the -\member{first} and \member{last} attributes are set in the -\class{Noddy} example. In the previous version of our module, the -instance variables \member{first} and \member{last} could be set to -non-string values or even deleted. We want to make sure that these -attributes always contain strings. - -\verbatiminput{noddy3.c} - -To provide greater control, over the \member{first} and \member{last} -attributes, we'll use custom getter and setter functions. Here are -the functions for getting and setting the \member{first} attribute: - -\begin{verbatim} -Noddy_getfirst(Noddy *self, void *closure) -{ - Py_INCREF(self->first); - return self->first; -} - -static int -Noddy_setfirst(Noddy *self, PyObject *value, void *closure) -{ - if (value == NULL) { - PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute"); - return -1; - } - - if (! PyString_Check(value)) { - PyErr_SetString(PyExc_TypeError, - "The first attribute value must be a string"); - return -1; - } - - Py_DECREF(self->first); - Py_INCREF(value); - self->first = value; - - return 0; -} -\end{verbatim} - -The getter function is passed a \class{Noddy} object and a -``closure'', which is void pointer. In this case, the closure is -ignored. (The closure supports an advanced usage in which definition -data is passed to the getter and setter. This could, for example, be -used to allow a single set of getter and setter functions that decide -the attribute to get or set based on data in the closure.) - -The setter function is passed the \class{Noddy} object, the new value, -and the closure. The new value may be \NULL, in which case the -attribute is being deleted. In our setter, we raise an error if the -attribute is deleted or if the attribute value is not a string. - -We create an array of \ctype{PyGetSetDef} structures: - -\begin{verbatim} -static PyGetSetDef Noddy_getseters[] = { - {"first", - (getter)Noddy_getfirst, (setter)Noddy_setfirst, - "first name", - NULL}, - {"last", - (getter)Noddy_getlast, (setter)Noddy_setlast, - "last name", - NULL}, - {NULL} /* Sentinel */ -}; -\end{verbatim} - -and register it in the \member{tp_getset} slot: - -\begin{verbatim} - Noddy_getseters, /* tp_getset */ -\end{verbatim} - -to register out attribute getters and setters. - -The last item in a \ctype{PyGetSetDef} structure is the closure -mentioned above. In this case, we aren't using the closure, so we just -pass \NULL. - -We also remove the member definitions for these attributes: - -\begin{verbatim} -static PyMemberDef Noddy_members[] = { - {"number", T_INT, offsetof(Noddy, number), 0, - "noddy number"}, - {NULL} /* Sentinel */ -}; -\end{verbatim} - -We also need to update the \member{tp_init} handler to only allow -strings\footnote{We now know that the first and last members are strings, -so perhaps we could be less careful about decrementing their -reference counts, however, we accept instances of string subclasses. -Even though deallocating normal strings won't call back into our -objects, we can't guarantee that deallocating an instance of a string -subclass won't. call back into out objects.} to be passed: - -\begin{verbatim} -static int -Noddy_init(Noddy *self, PyObject *args, PyObject *kwds) -{ - PyObject *first=NULL, *last=NULL, *tmp; - - static char *kwlist[] = {"first", "last", "number", NULL}; - - if (! PyArg_ParseTupleAndKeywords(args, kwds, "|SSi", kwlist, - &first, &last, - &self->number)) - return -1; - - if (first) { - tmp = self->first; - Py_INCREF(first); - self->first = first; - Py_DECREF(tmp); - } - - if (last) { - tmp = self->last; - Py_INCREF(last); - self->last = last; - Py_DECREF(tmp); - } - - return 0; -} -\end{verbatim} - -With these changes, we can assure that the \member{first} and -\member{last} members are never \NULL{} so we can remove checks for \NULL{} -values in almost all cases. This means that most of the -\cfunction{Py_XDECREF()} calls can be converted to \cfunction{Py_DECREF()} -calls. The only place we can't change these calls is in the -deallocator, where there is the possibility that the initialization of -these members failed in the constructor. - -We also rename the module initialization function and module name in -the initialization function, as we did before, and we add an extra -definition to the \file{setup.py} file. - -\subsection{Supporting cyclic garbage collection} - -Python has a cyclic-garbage collector that can identify unneeded -objects even when their reference counts are not zero. This can happen -when objects are involved in cycles. For example, consider: - -\begin{verbatim} ->>> l = [] ->>> l.append(l) ->>> del l -\end{verbatim} - -In this example, we create a list that contains itself. When we delete -it, it still has a reference from itself. Its reference count doesn't -drop to zero. Fortunately, Python's cyclic-garbage collector will -eventually figure out that the list is garbage and free it. - -In the second version of the \class{Noddy} example, we allowed any -kind of object to be stored in the \member{first} or \member{last} -attributes.\footnote{Even in the third version, we aren't guaranteed to -avoid cycles. Instances of string subclasses are allowed and string -subclasses could allow cycles even if normal strings don't.} This -means that \class{Noddy} objects can participate in cycles: - -\begin{verbatim} ->>> import noddy2 ->>> n = noddy2.Noddy() ->>> l = [n] ->>> n.first = l -\end{verbatim} - -This is pretty silly, but it gives us an excuse to add support for the -cyclic-garbage collector to the \class{Noddy} example. To support -cyclic garbage collection, types need to fill two slots and set a -class flag that enables these slots: - -\verbatiminput{noddy4.c} - -The traversal method provides access to subobjects that -could participate in cycles: - -\begin{verbatim} -static int -Noddy_traverse(Noddy *self, visitproc visit, void *arg) -{ - int vret; - - if (self->first) { - vret = visit(self->first, arg); - if (vret != 0) - return vret; - } - if (self->last) { - vret = visit(self->last, arg); - if (vret != 0) - return vret; - } - - return 0; -} -\end{verbatim} - -For each subobject that can participate in cycles, we need to call the -\cfunction{visit()} function, which is passed to the traversal method. -The \cfunction{visit()} function takes as arguments the subobject and -the extra argument \var{arg} passed to the traversal method. It -returns an integer value that must be returned if it is non-zero. - - -Python 2.4 and higher provide a \cfunction{Py_VISIT()} macro that automates -calling visit functions. With \cfunction{Py_VISIT()}, -\cfunction{Noddy_traverse()} can be simplified: - - -\begin{verbatim} -static int -Noddy_traverse(Noddy *self, visitproc visit, void *arg) -{ - Py_VISIT(self->first); - Py_VISIT(self->last); - return 0; -} -\end{verbatim} - -\note{Note that the \member{tp_traverse} implementation must name its - arguments exactly \var{visit} and \var{arg} in order to use - \cfunction{Py_VISIT()}. This is to encourage uniformity - across these boring implementations.} - -We also need to provide a method for clearing any subobjects that can -participate in cycles. We implement the method and reimplement the -deallocator to use it: - -\begin{verbatim} -static int -Noddy_clear(Noddy *self) -{ - PyObject *tmp; - - tmp = self->first; - self->first = NULL; - Py_XDECREF(tmp); - - tmp = self->last; - self->last = NULL; - Py_XDECREF(tmp); - - return 0; -} - -static void -Noddy_dealloc(Noddy* self) -{ - Noddy_clear(self); - self->ob_type->tp_free((PyObject*)self); -} -\end{verbatim} - -Notice the use of a temporary variable in \cfunction{Noddy_clear()}. -We use the temporary variable so that we can set each member to \NULL{} -before decrementing its reference count. We do this because, as was -discussed earlier, if the reference count drops to zero, we might -cause code to run that calls back into the object. In addition, -because we now support garbage collection, we also have to worry about -code being run that triggers garbage collection. If garbage -collection is run, our \member{tp_traverse} handler could get called. -We can't take a chance of having \cfunction{Noddy_traverse()} called -when a member's reference count has dropped to zero and its value -hasn't been set to \NULL. - -Python 2.4 and higher provide a \cfunction{Py_CLEAR()} that automates -the careful decrementing of reference counts. With -\cfunction{Py_CLEAR()}, the \cfunction{Noddy_clear()} function can be -simplified: - -\begin{verbatim} -static int -Noddy_clear(Noddy *self) -{ - Py_CLEAR(self->first); - Py_CLEAR(self->last); - return 0; -} -\end{verbatim} - -Finally, we add the \constant{Py_TPFLAGS_HAVE_GC} flag to the class -flags: - -\begin{verbatim} - Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC, /*tp_flags*/ -\end{verbatim} - -That's pretty much it. If we had written custom \member{tp_alloc} or -\member{tp_free} slots, we'd need to modify them for cyclic-garbage -collection. Most extensions will use the versions automatically -provided. - -\subsection{Subclassing other types} - -It is possible to create new extension types that are derived from existing -types. It is easiest to inherit from the built in types, since an extension -can easily use the \class{PyTypeObject} it needs. It can be difficult to -share these \class{PyTypeObject} structures between extension modules. - -In this example we will create a \class{Shoddy} type that inherits from -the builtin \class{list} type. The new type will be completely compatible -with regular lists, but will have an additional \method{increment()} method -that increases an internal counter. - -\begin{verbatim} ->>> import shoddy ->>> s = shoddy.Shoddy(range(3)) ->>> s.extend(s) ->>> print len(s) -6 ->>> print s.increment() -1 ->>> print s.increment() -2 -\end{verbatim} - -\verbatiminput{shoddy.c} - -As you can see, the source code closely resembles the \class{Noddy} examples in previous -sections. We will break down the main differences between them. - -\begin{verbatim} -typedef struct { - PyListObject list; - int state; -} Shoddy; -\end{verbatim} - -The primary difference for derived type objects is that the base type's -object structure must be the first value. The base type will already -include the \cfunction{PyObject_HEAD} at the beginning of its structure. - -When a Python object is a \class{Shoddy} instance, its \var{PyObject*} pointer -can be safely cast to both \var{PyListObject*} and \var{Shoddy*}. - -\begin{verbatim} -static int -Shoddy_init(Shoddy *self, PyObject *args, PyObject *kwds) -{ - if (PyList_Type.tp_init((PyObject *)self, args, kwds) < 0) - return -1; - self->state = 0; - return 0; -} -\end{verbatim} - -In the \member{__init__} method for our type, we can see how to call through -to the \member{__init__} method of the base type. - -This pattern is important when writing a type with custom \member{new} and -\member{dealloc} methods. The \member{new} method should not actually create the -memory for the object with \member{tp_alloc}, that will be handled by -the base class when calling its \member{tp_new}. - -When filling out the \cfunction{PyTypeObject} for the \class{Shoddy} type, -you see a slot for \cfunction{tp_base}. Due to cross platform compiler -issues, you can't fill that field directly with the \cfunction{PyList_Type}; -it can be done later in the module's \cfunction{init} function. - -\begin{verbatim} -PyMODINIT_FUNC -initshoddy(void) -{ - PyObject *m; - - ShoddyType.tp_base = &PyList_Type; - if (PyType_Ready(&ShoddyType) < 0) - return; - - m = Py_InitModule3("shoddy", NULL, "Shoddy module"); - if (m == NULL) - return; - - Py_INCREF(&ShoddyType); - PyModule_AddObject(m, "Shoddy", (PyObject *) &ShoddyType); -} -\end{verbatim} - -Before calling \cfunction{PyType_Ready}, the type structure must have the -\member{tp_base} slot filled in. When we are deriving a new type, it is -not necessary to fill out the \member{tp_alloc} slot with -\cfunction{PyType_GenericNew} -- the allocate function from the base type -will be inherited. - -After that, calling \cfunction{PyType_Ready} and adding the type object -to the module is the same as with the basic \class{Noddy} examples. - - -\section{Type Methods - \label{dnt-type-methods}} - -This section aims to give a quick fly-by on the various type methods -you can implement and what they do. - -Here is the definition of \ctype{PyTypeObject}, with some fields only -used in debug builds omitted: - -\verbatiminput{typestruct.h} - -Now that's a \emph{lot} of methods. Don't worry too much though - if -you have a type you want to define, the chances are very good that you -will only implement a handful of these. - -As you probably expect by now, we're going to go over this and give -more information about the various handlers. We won't go in the order -they are defined in the structure, because there is a lot of -historical baggage that impacts the ordering of the fields; be sure -your type initialization keeps the fields in the right order! It's -often easiest to find an example that includes all the fields you need -(even if they're initialized to \code{0}) and then change the values -to suit your new type. - -\begin{verbatim} - char *tp_name; /* For printing */ -\end{verbatim} - -The name of the type - as mentioned in the last section, this will -appear in various places, almost entirely for diagnostic purposes. -Try to choose something that will be helpful in such a situation! - -\begin{verbatim} - int tp_basicsize, tp_itemsize; /* For allocation */ -\end{verbatim} - -These fields tell the runtime how much memory to allocate when new -objects of this type are created. Python has some built-in support -for variable length structures (think: strings, lists) which is where -the \member{tp_itemsize} field comes in. This will be dealt with -later. - -\begin{verbatim} - char *tp_doc; -\end{verbatim} - -Here you can put a string (or its address) that you want returned when -the Python script references \code{obj.__doc__} to retrieve the -doc string. - -Now we come to the basic type methods---the ones most extension types -will implement. - - -\subsection{Finalization and De-allocation} - -\index{object!deallocation} -\index{deallocation, object} -\index{object!finalization} -\index{finalization, of objects} - -\begin{verbatim} - destructor tp_dealloc; -\end{verbatim} - -This function is called when the reference count of the instance of -your type is reduced to zero and the Python interpreter wants to -reclaim it. If your type has memory to free or other clean-up to -perform, put it here. The object itself needs to be freed here as -well. Here is an example of this function: - -\begin{verbatim} -static void -newdatatype_dealloc(newdatatypeobject * obj) -{ - free(obj->obj_UnderlyingDatatypePtr); - obj->ob_type->tp_free(obj); -} -\end{verbatim} - -One important requirement of the deallocator function is that it -leaves any pending exceptions alone. This is important since -deallocators are frequently called as the interpreter unwinds the -Python stack; when the stack is unwound due to an exception (rather -than normal returns), nothing is done to protect the deallocators from -seeing that an exception has already been set. Any actions which a -deallocator performs which may cause additional Python code to be -executed may detect that an exception has been set. This can lead to -misleading errors from the interpreter. The proper way to protect -against this is to save a pending exception before performing the -unsafe action, and restoring it when done. This can be done using the -\cfunction{PyErr_Fetch()}\ttindex{PyErr_Fetch()} and -\cfunction{PyErr_Restore()}\ttindex{PyErr_Restore()} functions: - -\begin{verbatim} -static void -my_dealloc(PyObject *obj) -{ - MyObject *self = (MyObject *) obj; - PyObject *cbresult; - - if (self->my_callback != NULL) { - PyObject *err_type, *err_value, *err_traceback; - int have_error = PyErr_Occurred() ? 1 : 0; - - if (have_error) - PyErr_Fetch(&err_type, &err_value, &err_traceback); - - cbresult = PyObject_CallObject(self->my_callback, NULL); - if (cbresult == NULL) - PyErr_WriteUnraisable(self->my_callback); - else - Py_DECREF(cbresult); - - if (have_error) - PyErr_Restore(err_type, err_value, err_traceback); - - Py_DECREF(self->my_callback); - } - obj->ob_type->tp_free((PyObject*)self); -} -\end{verbatim} - - -\subsection{Object Presentation} - -In Python, there are three ways to generate a textual representation -of an object: the \function{repr()}\bifuncindex{repr} function (or -equivalent back-tick syntax), the \function{str()}\bifuncindex{str} -function, and the \keyword{print} statement. For most objects, the -\keyword{print} statement is equivalent to the \function{str()} -function, but it is possible to special-case printing to a -\ctype{FILE*} if necessary; this should only be done if efficiency is -identified as a problem and profiling suggests that creating a -temporary string object to be written to a file is too expensive. - -These handlers are all optional, and most types at most need to -implement the \member{tp_str} and \member{tp_repr} handlers. - -\begin{verbatim} - reprfunc tp_repr; - reprfunc tp_str; - printfunc tp_print; -\end{verbatim} - -The \member{tp_repr} handler should return a string object containing -a representation of the instance for which it is called. Here is a -simple example: - -\begin{verbatim} -static PyObject * -newdatatype_repr(newdatatypeobject * obj) -{ - return PyString_FromFormat("Repr-ified_newdatatype{{size:\%d}}", - obj->obj_UnderlyingDatatypePtr->size); -} -\end{verbatim} - -If no \member{tp_repr} handler is specified, the interpreter will -supply a representation that uses the type's \member{tp_name} and a -uniquely-identifying value for the object. - -The \member{tp_str} handler is to \function{str()} what the -\member{tp_repr} handler described above is to \function{repr()}; that -is, it is called when Python code calls \function{str()} on an -instance of your object. Its implementation is very similar to the -\member{tp_repr} function, but the resulting string is intended for -human consumption. If \member{tp_str} is not specified, the -\member{tp_repr} handler is used instead. - -Here is a simple example: - -\begin{verbatim} -static PyObject * -newdatatype_str(newdatatypeobject * obj) -{ - return PyString_FromFormat("Stringified_newdatatype{{size:\%d}}", - obj->obj_UnderlyingDatatypePtr->size); -} -\end{verbatim} - -The print function will be called whenever Python needs to "print" an -instance of the type. For example, if 'node' is an instance of type -TreeNode, then the print function is called when Python code calls: - -\begin{verbatim} -print node -\end{verbatim} - -There is a flags argument and one flag, \constant{Py_PRINT_RAW}, and -it suggests that you print without string quotes and possibly without -interpreting escape sequences. - -The print function receives a file object as an argument. You will -likely want to write to that file object. - -Here is a sample print function: - -\begin{verbatim} -static int -newdatatype_print(newdatatypeobject *obj, FILE *fp, int flags) -{ - if (flags & Py_PRINT_RAW) { - fprintf(fp, "<{newdatatype object--size: %d}>", - obj->obj_UnderlyingDatatypePtr->size); - } - else { - fprintf(fp, "\"<{newdatatype object--size: %d}>\"", - obj->obj_UnderlyingDatatypePtr->size); - } - return 0; -} -\end{verbatim} - - -\subsection{Attribute Management} - -For every object which can support attributes, the corresponding type -must provide the functions that control how the attributes are -resolved. There needs to be a function which can retrieve attributes -(if any are defined), and another to set attributes (if setting -attributes is allowed). Removing an attribute is a special case, for -which the new value passed to the handler is \NULL. - -Python supports two pairs of attribute handlers; a type that supports -attributes only needs to implement the functions for one pair. The -difference is that one pair takes the name of the attribute as a -\ctype{char*}, while the other accepts a \ctype{PyObject*}. Each type -can use whichever pair makes more sense for the implementation's -convenience. - -\begin{verbatim} - getattrfunc tp_getattr; /* char * version */ - setattrfunc tp_setattr; - /* ... */ - getattrofunc tp_getattrofunc; /* PyObject * version */ - setattrofunc tp_setattrofunc; -\end{verbatim} - -If accessing attributes of an object is always a simple operation -(this will be explained shortly), there are generic implementations -which can be used to provide the \ctype{PyObject*} version of the -attribute management functions. The actual need for type-specific -attribute handlers almost completely disappeared starting with Python -2.2, though there are many examples which have not been updated to use -some of the new generic mechanism that is available. - - -\subsubsection{Generic Attribute Management} - -\versionadded{2.2} - -Most extension types only use \emph{simple} attributes. So, what -makes the attributes simple? There are only a couple of conditions -that must be met: - -\begin{enumerate} - \item The name of the attributes must be known when - \cfunction{PyType_Ready()} is called. - - \item No special processing is needed to record that an attribute - was looked up or set, nor do actions need to be taken based - on the value. -\end{enumerate} - -Note that this list does not place any restrictions on the values of -the attributes, when the values are computed, or how relevant data is -stored. - -When \cfunction{PyType_Ready()} is called, it uses three tables -referenced by the type object to create \emph{descriptors} which are -placed in the dictionary of the type object. Each descriptor controls -access to one attribute of the instance object. Each of the tables is -optional; if all three are \NULL, instances of the type will only have -attributes that are inherited from their base type, and should leave -the \member{tp_getattro} and \member{tp_setattro} fields \NULL{} as -well, allowing the base type to handle attributes. - -The tables are declared as three fields of the type object: - -\begin{verbatim} - struct PyMethodDef *tp_methods; - struct PyMemberDef *tp_members; - struct PyGetSetDef *tp_getset; -\end{verbatim} - -If \member{tp_methods} is not \NULL, it must refer to an array of -\ctype{PyMethodDef} structures. Each entry in the table is an -instance of this structure: - -\begin{verbatim} -typedef struct PyMethodDef { - char *ml_name; /* method name */ - PyCFunction ml_meth; /* implementation function */ - int ml_flags; /* flags */ - char *ml_doc; /* docstring */ -} PyMethodDef; -\end{verbatim} - -One entry should be defined for each method provided by the type; no -entries are needed for methods inherited from a base type. One -additional entry is needed at the end; it is a sentinel that marks the -end of the array. The \member{ml_name} field of the sentinel must be -\NULL. - -XXX Need to refer to some unified discussion of the structure fields, -shared with the next section. - -The second table is used to define attributes which map directly to -data stored in the instance. A variety of primitive C types are -supported, and access may be read-only or read-write. The structures -in the table are defined as: - -\begin{verbatim} -typedef struct PyMemberDef { - char *name; - int type; - int offset; - int flags; - char *doc; -} PyMemberDef; -\end{verbatim} - -For each entry in the table, a descriptor will be constructed and -added to the type which will be able to extract a value from the -instance structure. The \member{type} field should contain one of the -type codes defined in the \file{structmember.h} header; the value will -be used to determine how to convert Python values to and from C -values. The \member{flags} field is used to store flags which control -how the attribute can be accessed. - -XXX Need to move some of this to a shared section! - -The following flag constants are defined in \file{structmember.h}; -they may be combined using bitwise-OR. - -\begin{tableii}{l|l}{constant}{Constant}{Meaning} - \lineii{READONLY \ttindex{READONLY}} - {Never writable.} - \lineii{RO \ttindex{RO}} - {Shorthand for \constant{READONLY}.} - \lineii{READ_RESTRICTED \ttindex{READ_RESTRICTED}} - {Not readable in restricted mode.} - \lineii{WRITE_RESTRICTED \ttindex{WRITE_RESTRICTED}} - {Not writable in restricted mode.} - \lineii{RESTRICTED \ttindex{RESTRICTED}} - {Not readable or writable in restricted mode.} -\end{tableii} - -An interesting advantage of using the \member{tp_members} table to -build descriptors that are used at runtime is that any attribute -defined this way can have an associated doc string simply by providing -the text in the table. An application can use the introspection API -to retrieve the descriptor from the class object, and get the -doc string using its \member{__doc__} attribute. - -As with the \member{tp_methods} table, a sentinel entry with a -\member{name} value of \NULL{} is required. - - -% XXX Descriptors need to be explained in more detail somewhere, but -% not here. -% -% Descriptor objects have two handler functions which correspond to -% the \member{tp_getattro} and \member{tp_setattro} handlers. The -% \method{__get__()} handler is a function which is passed the -% descriptor, instance, and type objects, and returns the value of the -% attribute, or it returns \NULL{} and sets an exception. The -% \method{__set__()} handler is passed the descriptor, instance, type, -% and new value; - - -\subsubsection{Type-specific Attribute Management} - -For simplicity, only the \ctype{char*} version will be demonstrated -here; the type of the name parameter is the only difference between -the \ctype{char*} and \ctype{PyObject*} flavors of the interface. -This example effectively does the same thing as the generic example -above, but does not use the generic support added in Python 2.2. The -value in showing this is two-fold: it demonstrates how basic attribute -management can be done in a way that is portable to older versions of -Python, and explains how the handler functions are called, so that if -you do need to extend their functionality, you'll understand what -needs to be done. - -The \member{tp_getattr} handler is called when the object requires an -attribute look-up. It is called in the same situations where the -\method{__getattr__()} method of a class would be called. - -A likely way to handle this is (1) to implement a set of functions -(such as \cfunction{newdatatype_getSize()} and -\cfunction{newdatatype_setSize()} in the example below), (2) provide a -method table listing these functions, and (3) provide a getattr -function that returns the result of a lookup in that table. The -method table uses the same structure as the \member{tp_methods} field -of the type object. - -Here is an example: - -\begin{verbatim} -static PyMethodDef newdatatype_methods[] = { - {"getSize", (PyCFunction)newdatatype_getSize, METH_VARARGS, - "Return the current size."}, - {"setSize", (PyCFunction)newdatatype_setSize, METH_VARARGS, - "Set the size."}, - {NULL, NULL, 0, NULL} /* sentinel */ -}; - -static PyObject * -newdatatype_getattr(newdatatypeobject *obj, char *name) -{ - return Py_FindMethod(newdatatype_methods, (PyObject *)obj, name); -} -\end{verbatim} - -The \member{tp_setattr} handler is called when the -\method{__setattr__()} or \method{__delattr__()} method of a class -instance would be called. When an attribute should be deleted, the -third parameter will be \NULL. Here is an example that simply raises -an exception; if this were really all you wanted, the -\member{tp_setattr} handler should be set to \NULL. - -\begin{verbatim} -static int -newdatatype_setattr(newdatatypeobject *obj, char *name, PyObject *v) -{ - (void)PyErr_Format(PyExc_RuntimeError, "Read-only attribute: \%s", name); - return -1; -} -\end{verbatim} - - -\subsection{Object Comparison} - -\begin{verbatim} - cmpfunc tp_compare; -\end{verbatim} - -The \member{tp_compare} handler is called when comparisons are needed -and the object does not implement the specific rich comparison method -which matches the requested comparison. (It is always used if defined -and the \cfunction{PyObject_Compare()} or \cfunction{PyObject_Cmp()} -functions are used, or if \function{cmp()} is used from Python.) -It is analogous to the \method{__cmp__()} method. This function -should return \code{-1} if \var{obj1} is less than -\var{obj2}, \code{0} if they are equal, and \code{1} if -\var{obj1} is greater than -\var{obj2}. -(It was previously allowed to return arbitrary negative or positive -integers for less than and greater than, respectively; as of Python -2.2, this is no longer allowed. In the future, other return values -may be assigned a different meaning.) - -A \member{tp_compare} handler may raise an exception. In this case it -should return a negative value. The caller has to test for the -exception using \cfunction{PyErr_Occurred()}. - - -Here is a sample implementation: - -\begin{verbatim} -static int -newdatatype_compare(newdatatypeobject * obj1, newdatatypeobject * obj2) -{ - long result; - - if (obj1->obj_UnderlyingDatatypePtr->size < - obj2->obj_UnderlyingDatatypePtr->size) { - result = -1; - } - else if (obj1->obj_UnderlyingDatatypePtr->size > - obj2->obj_UnderlyingDatatypePtr->size) { - result = 1; - } - else { - result = 0; - } - return result; -} -\end{verbatim} - - -\subsection{Abstract Protocol Support} - -Python supports a variety of \emph{abstract} `protocols;' the specific -interfaces provided to use these interfaces are documented in the -\citetitle[../api/api.html]{Python/C API Reference Manual} in the -chapter ``\ulink{Abstract Objects Layer}{../api/abstract.html}.'' - -A number of these abstract interfaces were defined early in the -development of the Python implementation. In particular, the number, -mapping, and sequence protocols have been part of Python since the -beginning. Other protocols have been added over time. For protocols -which depend on several handler routines from the type implementation, -the older protocols have been defined as optional blocks of handlers -referenced by the type object. For newer protocols there are -additional slots in the main type object, with a flag bit being set to -indicate that the slots are present and should be checked by the -interpreter. (The flag bit does not indicate that the slot values are -non-\NULL. The flag may be set to indicate the presence of a slot, -but a slot may still be unfilled.) - -\begin{verbatim} - PyNumberMethods tp_as_number; - PySequenceMethods tp_as_sequence; - PyMappingMethods tp_as_mapping; -\end{verbatim} - -If you wish your object to be able to act like a number, a sequence, -or a mapping object, then you place the address of a structure that -implements the C type \ctype{PyNumberMethods}, -\ctype{PySequenceMethods}, or \ctype{PyMappingMethods}, respectively. -It is up to you to fill in this structure with appropriate values. You -can find examples of the use of each of these in the \file{Objects} -directory of the Python source distribution. - - -\begin{verbatim} - hashfunc tp_hash; -\end{verbatim} - -This function, if you choose to provide it, should return a hash -number for an instance of your data type. Here is a moderately -pointless example: - -\begin{verbatim} -static long -newdatatype_hash(newdatatypeobject *obj) -{ - long result; - result = obj->obj_UnderlyingDatatypePtr->size; - result = result * 3; - return result; -} -\end{verbatim} - -\begin{verbatim} - ternaryfunc tp_call; -\end{verbatim} - -This function is called when an instance of your data type is "called", -for example, if \code{obj1} is an instance of your data type and the Python -script contains \code{obj1('hello')}, the \member{tp_call} handler is -invoked. - -This function takes three arguments: - -\begin{enumerate} - \item - \var{arg1} is the instance of the data type which is the subject of - the call. If the call is \code{obj1('hello')}, then \var{arg1} is - \code{obj1}. - - \item - \var{arg2} is a tuple containing the arguments to the call. You - can use \cfunction{PyArg_ParseTuple()} to extract the arguments. - - \item - \var{arg3} is a dictionary of keyword arguments that were passed. - If this is non-\NULL{} and you support keyword arguments, use - \cfunction{PyArg_ParseTupleAndKeywords()} to extract the - arguments. If you do not want to support keyword arguments and - this is non-\NULL, raise a \exception{TypeError} with a message - saying that keyword arguments are not supported. -\end{enumerate} - -Here is a desultory example of the implementation of the call function. - -\begin{verbatim} -/* Implement the call function. - * obj1 is the instance receiving the call. - * obj2 is a tuple containing the arguments to the call, in this - * case 3 strings. - */ -static PyObject * -newdatatype_call(newdatatypeobject *obj, PyObject *args, PyObject *other) -{ - PyObject *result; - char *arg1; - char *arg2; - char *arg3; - - if (!PyArg_ParseTuple(args, "sss:call", &arg1, &arg2, &arg3)) { - return NULL; - } - result = PyString_FromFormat( - "Returning -- value: [\%d] arg1: [\%s] arg2: [\%s] arg3: [\%s]\n", - obj->obj_UnderlyingDatatypePtr->size, - arg1, arg2, arg3); - printf("\%s", PyString_AS_STRING(result)); - return result; -} -\end{verbatim} - -XXX some fields need to be added here... - - -\begin{verbatim} - /* Added in release 2.2 */ - /* Iterators */ - getiterfunc tp_iter; - iternextfunc tp_iternext; -\end{verbatim} - -These functions provide support for the iterator protocol. Any object -which wishes to support iteration over its contents (which may be -generated during iteration) must implement the \code{tp_iter} -handler. Objects which are returned by a \code{tp_iter} handler must -implement both the \code{tp_iter} and \code{tp_iternext} handlers. -Both handlers take exactly one parameter, the instance for which they -are being called, and return a new reference. In the case of an -error, they should set an exception and return \NULL. - -For an object which represents an iterable collection, the -\code{tp_iter} handler must return an iterator object. The iterator -object is responsible for maintaining the state of the iteration. For -collections which can support multiple iterators which do not -interfere with each other (as lists and tuples do), a new iterator -should be created and returned. Objects which can only be iterated -over once (usually due to side effects of iteration) should implement -this handler by returning a new reference to themselves, and should -also implement the \code{tp_iternext} handler. File objects are an -example of such an iterator. - -Iterator objects should implement both handlers. The \code{tp_iter} -handler should return a new reference to the iterator (this is the -same as the \code{tp_iter} handler for objects which can only be -iterated over destructively). The \code{tp_iternext} handler should -return a new reference to the next object in the iteration if there is -one. If the iteration has reached the end, it may return \NULL{} -without setting an exception or it may set \exception{StopIteration}; -avoiding the exception can yield slightly better performance. If an -actual error occurs, it should set an exception and return \NULL. - - -\subsection{Weak Reference Support\label{weakref-support}} - -One of the goals of Python's weak-reference implementation is to allow -any type to participate in the weak reference mechanism without -incurring the overhead on those objects which do not benefit by weak -referencing (such as numbers). - -For an object to be weakly referencable, the extension must include a -\ctype{PyObject*} field in the instance structure for the use of the -weak reference mechanism; it must be initialized to \NULL{} by the -object's constructor. It must also set the \member{tp_weaklistoffset} -field of the corresponding type object to the offset of the field. -For example, the instance type is defined with the following -structure: - -\begin{verbatim} -typedef struct { - PyObject_HEAD - PyClassObject *in_class; /* The class object */ - PyObject *in_dict; /* A dictionary */ - PyObject *in_weakreflist; /* List of weak references */ -} PyInstanceObject; -\end{verbatim} - -The statically-declared type object for instances is defined this way: - -\begin{verbatim} -PyTypeObject PyInstance_Type = { - PyObject_HEAD_INIT(&PyType_Type) - 0, - "module.instance", - - /* Lots of stuff omitted for brevity... */ - - Py_TPFLAGS_DEFAULT, /* tp_flags */ - 0, /* tp_doc */ - 0, /* tp_traverse */ - 0, /* tp_clear */ - 0, /* tp_richcompare */ - offsetof(PyInstanceObject, in_weakreflist), /* tp_weaklistoffset */ -}; -\end{verbatim} - -The type constructor is responsible for initializing the weak reference -list to \NULL: - -\begin{verbatim} -static PyObject * -instance_new() { - /* Other initialization stuff omitted for brevity */ - - self->in_weakreflist = NULL; - - return (PyObject *) self; -} -\end{verbatim} - -The only further addition is that the destructor needs to call the -weak reference manager to clear any weak references. This should be -done before any other parts of the destruction have occurred, but is -only required if the weak reference list is non-\NULL: - -\begin{verbatim} -static void -instance_dealloc(PyInstanceObject *inst) -{ - /* Allocate temporaries if needed, but do not begin - destruction just yet. - */ - - if (inst->in_weakreflist != NULL) - PyObject_ClearWeakRefs((PyObject *) inst); - - /* Proceed with object destruction normally. */ -} -\end{verbatim} - - -\subsection{More Suggestions} - -Remember that you can omit most of these functions, in which case you -provide \code{0} as a value. There are type definitions for each of -the functions you must provide. They are in \file{object.h} in the -Python include directory that comes with the source distribution of -Python. - -In order to learn how to implement any specific method for your new -data type, do the following: Download and unpack the Python source -distribution. Go the \file{Objects} directory, then search the -C source files for \code{tp_} plus the function you want (for -example, \code{tp_print} or \code{tp_compare}). You will find -examples of the function you want to implement. - -When you need to verify that an object is an instance of the type -you are implementing, use the \cfunction{PyObject_TypeCheck} function. -A sample of its use might be something like the following: - -\begin{verbatim} - if (! PyObject_TypeCheck(some_object, &MyType)) { - PyErr_SetString(PyExc_TypeError, "arg #1 not a mything"); - return NULL; - } -\end{verbatim} diff --git a/Doc/ext/noddy.c b/Doc/ext/noddy.c deleted file mode 100644 index ec2d669..0000000 --- a/Doc/ext/noddy.c +++ /dev/null @@ -1,54 +0,0 @@ -#include <Python.h> - -typedef struct { - PyObject_HEAD - /* Type-specific fields go here. */ -} noddy_NoddyObject; - -static PyTypeObject noddy_NoddyType = { - PyObject_HEAD_INIT(NULL) - 0, /*ob_size*/ - "noddy.Noddy", /*tp_name*/ - sizeof(noddy_NoddyObject), /*tp_basicsize*/ - 0, /*tp_itemsize*/ - 0, /*tp_dealloc*/ - 0, /*tp_print*/ - 0, /*tp_getattr*/ - 0, /*tp_setattr*/ - 0, /*tp_compare*/ - 0, /*tp_repr*/ - 0, /*tp_as_number*/ - 0, /*tp_as_sequence*/ - 0, /*tp_as_mapping*/ - 0, /*tp_hash */ - 0, /*tp_call*/ - 0, /*tp_str*/ - 0, /*tp_getattro*/ - 0, /*tp_setattro*/ - 0, /*tp_as_buffer*/ - Py_TPFLAGS_DEFAULT, /*tp_flags*/ - "Noddy objects", /* tp_doc */ -}; - -static PyMethodDef noddy_methods[] = { - {NULL} /* Sentinel */ -}; - -#ifndef PyMODINIT_FUNC /* declarations for DLL import/export */ -#define PyMODINIT_FUNC void -#endif -PyMODINIT_FUNC -initnoddy(void) -{ - PyObject* m; - - noddy_NoddyType.tp_new = PyType_GenericNew; - if (PyType_Ready(&noddy_NoddyType) < 0) - return; - - m = Py_InitModule3("noddy", noddy_methods, - "Example module that creates an extension type."); - - Py_INCREF(&noddy_NoddyType); - PyModule_AddObject(m, "Noddy", (PyObject *)&noddy_NoddyType); -} diff --git a/Doc/ext/noddy2.c b/Doc/ext/noddy2.c deleted file mode 100644 index 2caf985..0000000 --- a/Doc/ext/noddy2.c +++ /dev/null @@ -1,190 +0,0 @@ -#include <Python.h> -#include "structmember.h" - -typedef struct { - PyObject_HEAD - PyObject *first; /* first name */ - PyObject *last; /* last name */ - int number; -} Noddy; - -static void -Noddy_dealloc(Noddy* self) -{ - Py_XDECREF(self->first); - Py_XDECREF(self->last); - self->ob_type->tp_free((PyObject*)self); -} - -static PyObject * -Noddy_new(PyTypeObject *type, PyObject *args, PyObject *kwds) -{ - Noddy *self; - - self = (Noddy *)type->tp_alloc(type, 0); - if (self != NULL) { - self->first = PyString_FromString(""); - if (self->first == NULL) - { - Py_DECREF(self); - return NULL; - } - - self->last = PyString_FromString(""); - if (self->last == NULL) - { - Py_DECREF(self); - return NULL; - } - - self->number = 0; - } - - return (PyObject *)self; -} - -static int -Noddy_init(Noddy *self, PyObject *args, PyObject *kwds) -{ - PyObject *first=NULL, *last=NULL, *tmp; - - static char *kwlist[] = {"first", "last", "number", NULL}; - - if (! PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist, - &first, &last, - &self->number)) - return -1; - - if (first) { - tmp = self->first; - Py_INCREF(first); - self->first = first; - Py_XDECREF(tmp); - } - - if (last) { - tmp = self->last; - Py_INCREF(last); - self->last = last; - Py_XDECREF(tmp); - } - - return 0; -} - - -static PyMemberDef Noddy_members[] = { - {"first", T_OBJECT_EX, offsetof(Noddy, first), 0, - "first name"}, - {"last", T_OBJECT_EX, offsetof(Noddy, last), 0, - "last name"}, - {"number", T_INT, offsetof(Noddy, number), 0, - "noddy number"}, - {NULL} /* Sentinel */ -}; - -static PyObject * -Noddy_name(Noddy* self) -{ - static PyObject *format = NULL; - PyObject *args, *result; - - if (format == NULL) { - format = PyString_FromString("%s %s"); - if (format == NULL) - return NULL; - } - - if (self->first == NULL) { - PyErr_SetString(PyExc_AttributeError, "first"); - return NULL; - } - - if (self->last == NULL) { - PyErr_SetString(PyExc_AttributeError, "last"); - return NULL; - } - - args = Py_BuildValue("OO", self->first, self->last); - if (args == NULL) - return NULL; - - result = PyString_Format(format, args); - Py_DECREF(args); - - return result; -} - -static PyMethodDef Noddy_methods[] = { - {"name", (PyCFunction)Noddy_name, METH_NOARGS, - "Return the name, combining the first and last name" - }, - {NULL} /* Sentinel */ -}; - -static PyTypeObject NoddyType = { - PyObject_HEAD_INIT(NULL) - 0, /*ob_size*/ - "noddy.Noddy", /*tp_name*/ - sizeof(Noddy), /*tp_basicsize*/ - 0, /*tp_itemsize*/ - (destructor)Noddy_dealloc, /*tp_dealloc*/ - 0, /*tp_print*/ - 0, /*tp_getattr*/ - 0, /*tp_setattr*/ - 0, /*tp_compare*/ - 0, /*tp_repr*/ - 0, /*tp_as_number*/ - 0, /*tp_as_sequence*/ - 0, /*tp_as_mapping*/ - 0, /*tp_hash */ - 0, /*tp_call*/ - 0, /*tp_str*/ - 0, /*tp_getattro*/ - 0, /*tp_setattro*/ - 0, /*tp_as_buffer*/ - Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/ - "Noddy objects", /* tp_doc */ - 0, /* tp_traverse */ - 0, /* tp_clear */ - 0, /* tp_richcompare */ - 0, /* tp_weaklistoffset */ - 0, /* tp_iter */ - 0, /* tp_iternext */ - Noddy_methods, /* tp_methods */ - Noddy_members, /* tp_members */ - 0, /* tp_getset */ - 0, /* tp_base */ - 0, /* tp_dict */ - 0, /* tp_descr_get */ - 0, /* tp_descr_set */ - 0, /* tp_dictoffset */ - (initproc)Noddy_init, /* tp_init */ - 0, /* tp_alloc */ - Noddy_new, /* tp_new */ -}; - -static PyMethodDef module_methods[] = { - {NULL} /* Sentinel */ -}; - -#ifndef PyMODINIT_FUNC /* declarations for DLL import/export */ -#define PyMODINIT_FUNC void -#endif -PyMODINIT_FUNC -initnoddy2(void) -{ - PyObject* m; - - if (PyType_Ready(&NoddyType) < 0) - return; - - m = Py_InitModule3("noddy2", module_methods, - "Example module that creates an extension type."); - - if (m == NULL) - return; - - Py_INCREF(&NoddyType); - PyModule_AddObject(m, "Noddy", (PyObject *)&NoddyType); -} diff --git a/Doc/ext/noddy3.c b/Doc/ext/noddy3.c deleted file mode 100644 index 60260ad..0000000 --- a/Doc/ext/noddy3.c +++ /dev/null @@ -1,243 +0,0 @@ -#include <Python.h> -#include "structmember.h" - -typedef struct { - PyObject_HEAD - PyObject *first; - PyObject *last; - int number; -} Noddy; - -static void -Noddy_dealloc(Noddy* self) -{ - Py_XDECREF(self->first); - Py_XDECREF(self->last); - self->ob_type->tp_free((PyObject*)self); -} - -static PyObject * -Noddy_new(PyTypeObject *type, PyObject *args, PyObject *kwds) -{ - Noddy *self; - - self = (Noddy *)type->tp_alloc(type, 0); - if (self != NULL) { - self->first = PyString_FromString(""); - if (self->first == NULL) - { - Py_DECREF(self); - return NULL; - } - - self->last = PyString_FromString(""); - if (self->last == NULL) - { - Py_DECREF(self); - return NULL; - } - - self->number = 0; - } - - return (PyObject *)self; -} - -static int -Noddy_init(Noddy *self, PyObject *args, PyObject *kwds) -{ - PyObject *first=NULL, *last=NULL, *tmp; - - static char *kwlist[] = {"first", "last", "number", NULL}; - - if (! PyArg_ParseTupleAndKeywords(args, kwds, "|SSi", kwlist, - &first, &last, - &self->number)) - return -1; - - if (first) { - tmp = self->first; - Py_INCREF(first); - self->first = first; - Py_DECREF(tmp); - } - - if (last) { - tmp = self->last; - Py_INCREF(last); - self->last = last; - Py_DECREF(tmp); - } - - return 0; -} - -static PyMemberDef Noddy_members[] = { - {"number", T_INT, offsetof(Noddy, number), 0, - "noddy number"}, - {NULL} /* Sentinel */ -}; - -static PyObject * -Noddy_getfirst(Noddy *self, void *closure) -{ - Py_INCREF(self->first); - return self->first; -} - -static int -Noddy_setfirst(Noddy *self, PyObject *value, void *closure) -{ - if (value == NULL) { - PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute"); - return -1; - } - - if (! PyString_Check(value)) { - PyErr_SetString(PyExc_TypeError, - "The first attribute value must be a string"); - return -1; - } - - Py_DECREF(self->first); - Py_INCREF(value); - self->first = value; - - return 0; -} - -static PyObject * -Noddy_getlast(Noddy *self, void *closure) -{ - Py_INCREF(self->last); - return self->last; -} - -static int -Noddy_setlast(Noddy *self, PyObject *value, void *closure) -{ - if (value == NULL) { - PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute"); - return -1; - } - - if (! PyString_Check(value)) { - PyErr_SetString(PyExc_TypeError, - "The last attribute value must be a string"); - return -1; - } - - Py_DECREF(self->last); - Py_INCREF(value); - self->last = value; - - return 0; -} - -static PyGetSetDef Noddy_getseters[] = { - {"first", - (getter)Noddy_getfirst, (setter)Noddy_setfirst, - "first name", - NULL}, - {"last", - (getter)Noddy_getlast, (setter)Noddy_setlast, - "last name", - NULL}, - {NULL} /* Sentinel */ -}; - -static PyObject * -Noddy_name(Noddy* self) -{ - static PyObject *format = NULL; - PyObject *args, *result; - - if (format == NULL) { - format = PyString_FromString("%s %s"); - if (format == NULL) - return NULL; - } - - args = Py_BuildValue("OO", self->first, self->last); - if (args == NULL) - return NULL; - - result = PyString_Format(format, args); - Py_DECREF(args); - - return result; -} - -static PyMethodDef Noddy_methods[] = { - {"name", (PyCFunction)Noddy_name, METH_NOARGS, - "Return the name, combining the first and last name" - }, - {NULL} /* Sentinel */ -}; - -static PyTypeObject NoddyType = { - PyObject_HEAD_INIT(NULL) - 0, /*ob_size*/ - "noddy.Noddy", /*tp_name*/ - sizeof(Noddy), /*tp_basicsize*/ - 0, /*tp_itemsize*/ - (destructor)Noddy_dealloc, /*tp_dealloc*/ - 0, /*tp_print*/ - 0, /*tp_getattr*/ - 0, /*tp_setattr*/ - 0, /*tp_compare*/ - 0, /*tp_repr*/ - 0, /*tp_as_number*/ - 0, /*tp_as_sequence*/ - 0, /*tp_as_mapping*/ - 0, /*tp_hash */ - 0, /*tp_call*/ - 0, /*tp_str*/ - 0, /*tp_getattro*/ - 0, /*tp_setattro*/ - 0, /*tp_as_buffer*/ - Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/ - "Noddy objects", /* tp_doc */ - 0, /* tp_traverse */ - 0, /* tp_clear */ - 0, /* tp_richcompare */ - 0, /* tp_weaklistoffset */ - 0, /* tp_iter */ - 0, /* tp_iternext */ - Noddy_methods, /* tp_methods */ - Noddy_members, /* tp_members */ - Noddy_getseters, /* tp_getset */ - 0, /* tp_base */ - 0, /* tp_dict */ - 0, /* tp_descr_get */ - 0, /* tp_descr_set */ - 0, /* tp_dictoffset */ - (initproc)Noddy_init, /* tp_init */ - 0, /* tp_alloc */ - Noddy_new, /* tp_new */ -}; - -static PyMethodDef module_methods[] = { - {NULL} /* Sentinel */ -}; - -#ifndef PyMODINIT_FUNC /* declarations for DLL import/export */ -#define PyMODINIT_FUNC void -#endif -PyMODINIT_FUNC -initnoddy3(void) -{ - PyObject* m; - - if (PyType_Ready(&NoddyType) < 0) - return; - - m = Py_InitModule3("noddy3", module_methods, - "Example module that creates an extension type."); - - if (m == NULL) - return; - - Py_INCREF(&NoddyType); - PyModule_AddObject(m, "Noddy", (PyObject *)&NoddyType); -} diff --git a/Doc/ext/noddy4.c b/Doc/ext/noddy4.c deleted file mode 100644 index 878e086..0000000 --- a/Doc/ext/noddy4.c +++ /dev/null @@ -1,224 +0,0 @@ -#include <Python.h> -#include "structmember.h" - -typedef struct { - PyObject_HEAD - PyObject *first; - PyObject *last; - int number; -} Noddy; - -static int -Noddy_traverse(Noddy *self, visitproc visit, void *arg) -{ - int vret; - - if (self->first) { - vret = visit(self->first, arg); - if (vret != 0) - return vret; - } - if (self->last) { - vret = visit(self->last, arg); - if (vret != 0) - return vret; - } - - return 0; -} - -static int -Noddy_clear(Noddy *self) -{ - PyObject *tmp; - - tmp = self->first; - self->first = NULL; - Py_XDECREF(tmp); - - tmp = self->last; - self->last = NULL; - Py_XDECREF(tmp); - - return 0; -} - -static void -Noddy_dealloc(Noddy* self) -{ - Noddy_clear(self); - self->ob_type->tp_free((PyObject*)self); -} - -static PyObject * -Noddy_new(PyTypeObject *type, PyObject *args, PyObject *kwds) -{ - Noddy *self; - - self = (Noddy *)type->tp_alloc(type, 0); - if (self != NULL) { - self->first = PyString_FromString(""); - if (self->first == NULL) - { - Py_DECREF(self); - return NULL; - } - - self->last = PyString_FromString(""); - if (self->last == NULL) - { - Py_DECREF(self); - return NULL; - } - - self->number = 0; - } - - return (PyObject *)self; -} - -static int -Noddy_init(Noddy *self, PyObject *args, PyObject *kwds) -{ - PyObject *first=NULL, *last=NULL, *tmp; - - static char *kwlist[] = {"first", "last", "number", NULL}; - - if (! PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist, - &first, &last, - &self->number)) - return -1; - - if (first) { - tmp = self->first; - Py_INCREF(first); - self->first = first; - Py_XDECREF(tmp); - } - - if (last) { - tmp = self->last; - Py_INCREF(last); - self->last = last; - Py_XDECREF(tmp); - } - - return 0; -} - - -static PyMemberDef Noddy_members[] = { - {"first", T_OBJECT_EX, offsetof(Noddy, first), 0, - "first name"}, - {"last", T_OBJECT_EX, offsetof(Noddy, last), 0, - "last name"}, - {"number", T_INT, offsetof(Noddy, number), 0, - "noddy number"}, - {NULL} /* Sentinel */ -}; - -static PyObject * -Noddy_name(Noddy* self) -{ - static PyObject *format = NULL; - PyObject *args, *result; - - if (format == NULL) { - format = PyString_FromString("%s %s"); - if (format == NULL) - return NULL; - } - - if (self->first == NULL) { - PyErr_SetString(PyExc_AttributeError, "first"); - return NULL; - } - - if (self->last == NULL) { - PyErr_SetString(PyExc_AttributeError, "last"); - return NULL; - } - - args = Py_BuildValue("OO", self->first, self->last); - if (args == NULL) - return NULL; - - result = PyString_Format(format, args); - Py_DECREF(args); - - return result; -} - -static PyMethodDef Noddy_methods[] = { - {"name", (PyCFunction)Noddy_name, METH_NOARGS, - "Return the name, combining the first and last name" - }, - {NULL} /* Sentinel */ -}; - -static PyTypeObject NoddyType = { - PyObject_HEAD_INIT(NULL) - 0, /*ob_size*/ - "noddy.Noddy", /*tp_name*/ - sizeof(Noddy), /*tp_basicsize*/ - 0, /*tp_itemsize*/ - (destructor)Noddy_dealloc, /*tp_dealloc*/ - 0, /*tp_print*/ - 0, /*tp_getattr*/ - 0, /*tp_setattr*/ - 0, /*tp_compare*/ - 0, /*tp_repr*/ - 0, /*tp_as_number*/ - 0, /*tp_as_sequence*/ - 0, /*tp_as_mapping*/ - 0, /*tp_hash */ - 0, /*tp_call*/ - 0, /*tp_str*/ - 0, /*tp_getattro*/ - 0, /*tp_setattro*/ - 0, /*tp_as_buffer*/ - Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC, /*tp_flags*/ - "Noddy objects", /* tp_doc */ - (traverseproc)Noddy_traverse, /* tp_traverse */ - (inquiry)Noddy_clear, /* tp_clear */ - 0, /* tp_richcompare */ - 0, /* tp_weaklistoffset */ - 0, /* tp_iter */ - 0, /* tp_iternext */ - Noddy_methods, /* tp_methods */ - Noddy_members, /* tp_members */ - 0, /* tp_getset */ - 0, /* tp_base */ - 0, /* tp_dict */ - 0, /* tp_descr_get */ - 0, /* tp_descr_set */ - 0, /* tp_dictoffset */ - (initproc)Noddy_init, /* tp_init */ - 0, /* tp_alloc */ - Noddy_new, /* tp_new */ -}; - -static PyMethodDef module_methods[] = { - {NULL} /* Sentinel */ -}; - -#ifndef PyMODINIT_FUNC /* declarations for DLL import/export */ -#define PyMODINIT_FUNC void -#endif -PyMODINIT_FUNC -initnoddy4(void) -{ - PyObject* m; - - if (PyType_Ready(&NoddyType) < 0) - return; - - m = Py_InitModule3("noddy4", module_methods, - "Example module that creates an extension type."); - - if (m == NULL) - return; - - Py_INCREF(&NoddyType); - PyModule_AddObject(m, "Noddy", (PyObject *)&NoddyType); -} diff --git a/Doc/ext/run-func.c b/Doc/ext/run-func.c deleted file mode 100644 index 5a7df0d..0000000 --- a/Doc/ext/run-func.c +++ /dev/null @@ -1,68 +0,0 @@ -#include <Python.h> - -int -main(int argc, char *argv[]) -{ - PyObject *pName, *pModule, *pDict, *pFunc; - PyObject *pArgs, *pValue; - int i; - - if (argc < 3) { - fprintf(stderr,"Usage: call pythonfile funcname [args]\n"); - return 1; - } - - Py_Initialize(); - pName = PyString_FromString(argv[1]); - /* Error checking of pName left out */ - - pModule = PyImport_Import(pName); - Py_DECREF(pName); - - if (pModule != NULL) { - pFunc = PyObject_GetAttrString(pModule, argv[2]); - /* pFunc is a new reference */ - - if (pFunc && PyCallable_Check(pFunc)) { - pArgs = PyTuple_New(argc - 3); - for (i = 0; i < argc - 3; ++i) { - pValue = PyInt_FromLong(atoi(argv[i + 3])); - if (!pValue) { - Py_DECREF(pArgs); - Py_DECREF(pModule); - fprintf(stderr, "Cannot convert argument\n"); - return 1; - } - /* pValue reference stolen here: */ - PyTuple_SetItem(pArgs, i, pValue); - } - pValue = PyObject_CallObject(pFunc, pArgs); - Py_DECREF(pArgs); - if (pValue != NULL) { - printf("Result of call: %ld\n", PyInt_AsLong(pValue)); - Py_DECREF(pValue); - } - else { - Py_DECREF(pFunc); - Py_DECREF(pModule); - PyErr_Print(); - fprintf(stderr,"Call failed\n"); - return 1; - } - } - else { - if (PyErr_Occurred()) - PyErr_Print(); - fprintf(stderr, "Cannot find function \"%s\"\n", argv[2]); - } - Py_XDECREF(pFunc); - Py_DECREF(pModule); - } - else { - PyErr_Print(); - fprintf(stderr, "Failed to load \"%s\"\n", argv[1]); - return 1; - } - Py_Finalize(); - return 0; -} diff --git a/Doc/ext/setup.py b/Doc/ext/setup.py deleted file mode 100644 index b853d23..0000000 --- a/Doc/ext/setup.py +++ /dev/null @@ -1,8 +0,0 @@ -from distutils.core import setup, Extension -setup(name="noddy", version="1.0", - ext_modules=[ - Extension("noddy", ["noddy.c"]), - Extension("noddy2", ["noddy2.c"]), - Extension("noddy3", ["noddy3.c"]), - Extension("noddy4", ["noddy4.c"]), - ]) diff --git a/Doc/ext/shoddy.c b/Doc/ext/shoddy.c deleted file mode 100644 index 07a4177..0000000 --- a/Doc/ext/shoddy.c +++ /dev/null @@ -1,91 +0,0 @@ -#include <Python.h> - -typedef struct { - PyListObject list; - int state; -} Shoddy; - - -static PyObject * -Shoddy_increment(Shoddy *self, PyObject *unused) -{ - self->state++; - return PyInt_FromLong(self->state); -} - - -static PyMethodDef Shoddy_methods[] = { - {"increment", (PyCFunction)Shoddy_increment, METH_NOARGS, - PyDoc_STR("increment state counter")}, - {NULL, NULL}, -}; - -static int -Shoddy_init(Shoddy *self, PyObject *args, PyObject *kwds) -{ - if (PyList_Type.tp_init((PyObject *)self, args, kwds) < 0) - return -1; - self->state = 0; - return 0; -} - - -static PyTypeObject ShoddyType = { - PyObject_HEAD_INIT(NULL) - 0, /* ob_size */ - "shoddy.Shoddy", /* tp_name */ - sizeof(Shoddy), /* tp_basicsize */ - 0, /* tp_itemsize */ - 0, /* tp_dealloc */ - 0, /* tp_print */ - 0, /* tp_getattr */ - 0, /* tp_setattr */ - 0, /* tp_compare */ - 0, /* tp_repr */ - 0, /* tp_as_number */ - 0, /* tp_as_sequence */ - 0, /* tp_as_mapping */ - 0, /* tp_hash */ - 0, /* tp_call */ - 0, /* tp_str */ - 0, /* tp_getattro */ - 0, /* tp_setattro */ - 0, /* tp_as_buffer */ - Py_TPFLAGS_DEFAULT | - Py_TPFLAGS_BASETYPE, /* tp_flags */ - 0, /* tp_doc */ - 0, /* tp_traverse */ - 0, /* tp_clear */ - 0, /* tp_richcompare */ - 0, /* tp_weaklistoffset */ - 0, /* tp_iter */ - 0, /* tp_iternext */ - Shoddy_methods, /* tp_methods */ - 0, /* tp_members */ - 0, /* tp_getset */ - 0, /* tp_base */ - 0, /* tp_dict */ - 0, /* tp_descr_get */ - 0, /* tp_descr_set */ - 0, /* tp_dictoffset */ - (initproc)Shoddy_init, /* tp_init */ - 0, /* tp_alloc */ - 0, /* tp_new */ -}; - -PyMODINIT_FUNC -initshoddy(void) -{ - PyObject *m; - - ShoddyType.tp_base = &PyList_Type; - if (PyType_Ready(&ShoddyType) < 0) - return; - - m = Py_InitModule3("shoddy", NULL, "Shoddy module"); - if (m == NULL) - return; - - Py_INCREF(&ShoddyType); - PyModule_AddObject(m, "Shoddy", (PyObject *) &ShoddyType); -} diff --git a/Doc/ext/test.py b/Doc/ext/test.py deleted file mode 100644 index 7ebf46a..0000000 --- a/Doc/ext/test.py +++ /dev/null @@ -1,213 +0,0 @@ -"""Test module for the noddy examples - -Noddy 1: - ->>> import noddy ->>> n1 = noddy.Noddy() ->>> n2 = noddy.Noddy() ->>> del n1 ->>> del n2 - - -Noddy 2 - ->>> import noddy2 ->>> n1 = noddy2.Noddy('jim', 'fulton', 42) ->>> n1.first -'jim' ->>> n1.last -'fulton' ->>> n1.number -42 ->>> n1.name() -'jim fulton' ->>> n1.first = 'will' ->>> n1.name() -'will fulton' ->>> n1.last = 'tell' ->>> n1.name() -'will tell' ->>> del n1.first ->>> n1.name() -Traceback (most recent call last): -... -AttributeError: first ->>> n1.first -Traceback (most recent call last): -... -AttributeError: first ->>> n1.first = 'drew' ->>> n1.first -'drew' ->>> del n1.number -Traceback (most recent call last): -... -TypeError: can't delete numeric/char attribute ->>> n1.number=2 ->>> n1.number -2 ->>> n1.first = 42 ->>> n1.name() -'42 tell' ->>> n2 = noddy2.Noddy() ->>> n2.name() -' ' ->>> n2.first -'' ->>> n2.last -'' ->>> del n2.first ->>> n2.first -Traceback (most recent call last): -... -AttributeError: first ->>> n2.first -Traceback (most recent call last): -... -AttributeError: first ->>> n2.name() -Traceback (most recent call last): - File "<stdin>", line 1, in ? -AttributeError: first ->>> n2.number -0 ->>> n3 = noddy2.Noddy('jim', 'fulton', 'waaa') -Traceback (most recent call last): - File "<stdin>", line 1, in ? -TypeError: an integer is required ->>> del n1 ->>> del n2 - - -Noddy 3 - ->>> import noddy3 ->>> n1 = noddy3.Noddy('jim', 'fulton', 42) ->>> n1 = noddy3.Noddy('jim', 'fulton', 42) ->>> n1.name() -'jim fulton' ->>> del n1.first -Traceback (most recent call last): - File "<stdin>", line 1, in ? -TypeError: Cannot delete the first attribute ->>> n1.first = 42 -Traceback (most recent call last): - File "<stdin>", line 1, in ? -TypeError: The first attribute value must be a string ->>> n1.first = 'will' ->>> n1.name() -'will fulton' ->>> n2 = noddy3.Noddy() ->>> n2 = noddy3.Noddy() ->>> n2 = noddy3.Noddy() ->>> n3 = noddy3.Noddy('jim', 'fulton', 'waaa') -Traceback (most recent call last): - File "<stdin>", line 1, in ? -TypeError: an integer is required ->>> del n1 ->>> del n2 - -Noddy 4 - ->>> import noddy4 ->>> n1 = noddy4.Noddy('jim', 'fulton', 42) ->>> n1.first -'jim' ->>> n1.last -'fulton' ->>> n1.number -42 ->>> n1.name() -'jim fulton' ->>> n1.first = 'will' ->>> n1.name() -'will fulton' ->>> n1.last = 'tell' ->>> n1.name() -'will tell' ->>> del n1.first ->>> n1.name() -Traceback (most recent call last): -... -AttributeError: first ->>> n1.first -Traceback (most recent call last): -... -AttributeError: first ->>> n1.first = 'drew' ->>> n1.first -'drew' ->>> del n1.number -Traceback (most recent call last): -... -TypeError: can't delete numeric/char attribute ->>> n1.number=2 ->>> n1.number -2 ->>> n1.first = 42 ->>> n1.name() -'42 tell' ->>> n2 = noddy4.Noddy() ->>> n2 = noddy4.Noddy() ->>> n2 = noddy4.Noddy() ->>> n2 = noddy4.Noddy() ->>> n2.name() -' ' ->>> n2.first -'' ->>> n2.last -'' ->>> del n2.first ->>> n2.first -Traceback (most recent call last): -... -AttributeError: first ->>> n2.first -Traceback (most recent call last): -... -AttributeError: first ->>> n2.name() -Traceback (most recent call last): - File "<stdin>", line 1, in ? -AttributeError: first ->>> n2.number -0 ->>> n3 = noddy4.Noddy('jim', 'fulton', 'waaa') -Traceback (most recent call last): - File "<stdin>", line 1, in ? -TypeError: an integer is required - - -Test cyclic gc(?) - ->>> import gc ->>> gc.disable() - ->>> x = [] ->>> l = [x] ->>> n2.first = l ->>> n2.first -[[]] ->>> l.append(n2) ->>> del l ->>> del n1 ->>> del n2 ->>> sys.getrefcount(x) -3 ->>> ignore = gc.collect() ->>> sys.getrefcount(x) -2 - ->>> gc.enable() -""" - -import os -import sys -from distutils.util import get_platform -PLAT_SPEC = "%s-%s" % (get_platform(), sys.version[0:3]) -src = os.path.join("build", "lib.%s" % PLAT_SPEC) -sys.path.append(src) - -if __name__ == "__main__": - import doctest, __main__ - doctest.testmod(__main__) diff --git a/Doc/ext/windows.tex b/Doc/ext/windows.tex deleted file mode 100644 index f9de548..0000000 --- a/Doc/ext/windows.tex +++ /dev/null @@ -1,320 +0,0 @@ -\chapter{Building C and \Cpp{} Extensions on Windows% - \label{building-on-windows}} - - -This chapter briefly explains how to create a Windows extension module -for Python using Microsoft Visual \Cpp, and follows with more -detailed background information on how it works. The explanatory -material is useful for both the Windows programmer learning to build -Python extensions and the \UNIX{} programmer interested in producing -software which can be successfully built on both \UNIX{} and Windows. - -Module authors are encouraged to use the distutils approach for -building extension modules, instead of the one described in this -section. You will still need the C compiler that was used to build -Python; typically Microsoft Visual \Cpp. - -\begin{notice} - This chapter mentions a number of filenames that include an encoded - Python version number. These filenames are represented with the - version number shown as \samp{XY}; in practive, \character{X} will - be the major version number and \character{Y} will be the minor - version number of the Python release you're working with. For - example, if you are using Python 2.2.1, \samp{XY} will actually be - \samp{22}. -\end{notice} - - -\section{A Cookbook Approach \label{win-cookbook}} - -There are two approaches to building extension modules on Windows, -just as there are on \UNIX: use the -\ulink{\module{distutils}}{../lib/module-distutils.html} package to -control the build process, or do things manually. The distutils -approach works well for most extensions; documentation on using -\ulink{\module{distutils}}{../lib/module-distutils.html} to build and -package extension modules is available in -\citetitle[../dist/dist.html]{Distributing Python Modules}. This -section describes the manual approach to building Python extensions -written in C or \Cpp. - -To build extensions using these instructions, you need to have a copy -of the Python sources of the same version as your installed Python. -You will need Microsoft Visual \Cpp{} ``Developer Studio''; project -files are supplied for V\Cpp{} version 7.1, but you can use older -versions of V\Cpp. Notice that you should use the same version of -V\Cpp that was used to build Python itself. The example files -described here are distributed with the Python sources in the -\file{PC\textbackslash example_nt\textbackslash} directory. - -\begin{enumerate} - \item - \strong{Copy the example files}\\ - The \file{example_nt} directory is a subdirectory of the \file{PC} - directory, in order to keep all the PC-specific files under the - same directory in the source distribution. However, the - \file{example_nt} directory can't actually be used from this - location. You first need to copy or move it up one level, so that - \file{example_nt} is a sibling of the \file{PC} and \file{Include} - directories. Do all your work from within this new location. - - \item - \strong{Open the project}\\ - From V\Cpp, use the \menuselection{File \sub Open Solution} - dialog (not \menuselection{File \sub Open}!). Navigate to and - select the file \file{example.sln}, in the \emph{copy} of the - \file{example_nt} directory you made above. Click Open. - - \item - \strong{Build the example DLL}\\ - In order to check that everything is set up right, try building: - - \begin{enumerate} - \item - Select a configuration. This step is optional. Choose - \menuselection{Build \sub Configuration Manager \sub Active - Solution Configuration} and select either \guilabel{Release} - or\guilabel{Debug}. If you skip this step, - V\Cpp{} will use the Debug configuration by default. - - \item - Build the DLL. Choose \menuselection{Build \sub Build - Solution}. This creates all intermediate and result files in - a subdirectory called either \file{Debug} or \file{Release}, - depending on which configuration you selected in the preceding - step. - \end{enumerate} - - \item - \strong{Testing the debug-mode DLL}\\ - Once the Debug build has succeeded, bring up a DOS box, and change - to the \file{example_nt\textbackslash Debug} directory. You - should now be able to repeat the following session (\code{C>} is - the DOS prompt, \code{>>>} is the Python prompt; note that - build information and various debug output from Python may not - match this screen dump exactly): - -\begin{verbatim} -C>..\..\PCbuild\python_d -Adding parser accelerators ... -Done. -Python 2.2 (#28, Dec 19 2001, 23:26:37) [MSC 32 bit (Intel)] on win32 -Type "copyright", "credits" or "license" for more information. ->>> import example -[4897 refs] ->>> example.foo() -Hello, world -[4903 refs] ->>> -\end{verbatim} - - Congratulations! You've successfully built your first Python - extension module. - - \item - \strong{Creating your own project}\\ - Choose a name and create a directory for it. Copy your C sources - into it. Note that the module source file name does not - necessarily have to match the module name, but the name of the - initialization function should match the module name --- you can - only import a module \module{spam} if its initialization function - is called \cfunction{initspam()}, and it should call - \cfunction{Py_InitModule()} with the string \code{"spam"} as its - first argument (use the minimal \file{example.c} in this directory - as a guide). By convention, it lives in a file called - \file{spam.c} or \file{spammodule.c}. The output file should be - called \file{spam.dll} or \file{spam.pyd} (the latter is supported - to avoid confusion with a system library \file{spam.dll} to which - your module could be a Python interface) in Release mode, or - \file{spam_d.dll} or \file{spam_d.pyd} in Debug mode. - - Now your options are: - - \begin{enumerate} - \item Copy \file{example.sln} and \file{example.vcproj}, rename - them to \file{spam.*}, and edit them by hand, or - \item Create a brand new project; instructions are below. - \end{enumerate} - - In either case, copy \file{example_nt\textbackslash example.def} - to \file{spam\textbackslash spam.def}, and edit the new - \file{spam.def} so its second line contains the string - `\code{initspam}'. If you created a new project yourself, add the - file \file{spam.def} to the project now. (This is an annoying - little file with only two lines. An alternative approach is to - forget about the \file{.def} file, and add the option - \programopt{/export:initspam} somewhere to the Link settings, by - manually editing the setting in Project Properties dialog). - - \item - \strong{Creating a brand new project}\\ - Use the \menuselection{File \sub New \sub Project} dialog to - create a new Project Workspace. Select \guilabel{Visual C++ - Projects/Win32/ Win32 Project}, enter the name (\samp{spam}), and - make sure the Location is set to parent of the \file{spam} - directory you have created (which should be a direct subdirectory - of the Python build tree, a sibling of \file{Include} and - \file{PC}). Select Win32 as the platform (in my version, this is - the only choice). Make sure the Create new workspace radio button - is selected. Click OK. - - You should now create the file \file{spam.def} as instructed in - the previous section. Add the source files to the project, using - \menuselection{Project \sub Add Existing Item}. Set the pattern to - \code{*.*} and select both \file{spam.c} and \file{spam.def} and - click OK. (Inserting them one by one is fine too.) - - Now open the \menuselection{Project \sub spam properties} dialog. - You only need to change a few settings. Make sure \guilabel{All - Configurations} is selected from the \guilabel{Settings for:} - dropdown list. Select the C/\Cpp{} tab. Choose the General - category in the popup menu at the top. Type the following text in - the entry box labeled \guilabel{Additional Include Directories}: - -\begin{verbatim} -..\Include,..\PC -\end{verbatim} - - Then, choose the General category in the Linker tab, and enter - -\begin{verbatim} -..\PCbuild -\end{verbatim} - - in the text box labelled \guilabel{Additional library Directories}. - - Now you need to add some mode-specific settings: - - Select \guilabel{Release} in the \guilabel{Configuration} - dropdown list. Choose the \guilabel{Link} tab, choose the - \guilabel{Input} category, and append \code{pythonXY.lib} to the - list in the \guilabel{Additional Dependencies} box. - - Select \guilabel{Debug} in the \guilabel{Configuration} dropdown - list, and append \code{pythonXY_d.lib} to the list in the - \guilabel{Additional Dependencies} box. Then click the C/\Cpp{} - tab, select \guilabel{Code Generation}, and select - \guilabel{Multi-threaded Debug DLL} from the \guilabel{Runtime - library} dropdown list. - - Select \guilabel{Release} again from the \guilabel{Configuration} - dropdown list. Select \guilabel{Multi-threaded DLL} from the - \guilabel{Runtime library} dropdown list. -\end{enumerate} - - -If your module creates a new type, you may have trouble with this line: - -\begin{verbatim} - PyObject_HEAD_INIT(&PyType_Type) -\end{verbatim} - -Change it to: - -\begin{verbatim} - PyObject_HEAD_INIT(NULL) -\end{verbatim} - -and add the following to the module initialization function: - -\begin{verbatim} - MyObject_Type.ob_type = &PyType_Type; -\end{verbatim} - -Refer to section~3 of the -\citetitle[http://www.python.org/doc/FAQ.html]{Python FAQ} for details -on why you must do this. - - -\section{Differences Between \UNIX{} and Windows - \label{dynamic-linking}} -\sectionauthor{Chris Phoenix}{cphoenix@best.com} - - -\UNIX{} and Windows use completely different paradigms for run-time -loading of code. Before you try to build a module that can be -dynamically loaded, be aware of how your system works. - -In \UNIX, a shared object (\file{.so}) file contains code to be used by the -program, and also the names of functions and data that it expects to -find in the program. When the file is joined to the program, all -references to those functions and data in the file's code are changed -to point to the actual locations in the program where the functions -and data are placed in memory. This is basically a link operation. - -In Windows, a dynamic-link library (\file{.dll}) file has no dangling -references. Instead, an access to functions or data goes through a -lookup table. So the DLL code does not have to be fixed up at runtime -to refer to the program's memory; instead, the code already uses the -DLL's lookup table, and the lookup table is modified at runtime to -point to the functions and data. - -In \UNIX, there is only one type of library file (\file{.a}) which -contains code from several object files (\file{.o}). During the link -step to create a shared object file (\file{.so}), the linker may find -that it doesn't know where an identifier is defined. The linker will -look for it in the object files in the libraries; if it finds it, it -will include all the code from that object file. - -In Windows, there are two types of library, a static library and an -import library (both called \file{.lib}). A static library is like a -\UNIX{} \file{.a} file; it contains code to be included as necessary. -An import library is basically used only to reassure the linker that a -certain identifier is legal, and will be present in the program when -the DLL is loaded. So the linker uses the information from the -import library to build the lookup table for using identifiers that -are not included in the DLL. When an application or a DLL is linked, -an import library may be generated, which will need to be used for all -future DLLs that depend on the symbols in the application or DLL. - -Suppose you are building two dynamic-load modules, B and C, which should -share another block of code A. On \UNIX, you would \emph{not} pass -\file{A.a} to the linker for \file{B.so} and \file{C.so}; that would -cause it to be included twice, so that B and C would each have their -own copy. In Windows, building \file{A.dll} will also build -\file{A.lib}. You \emph{do} pass \file{A.lib} to the linker for B and -C. \file{A.lib} does not contain code; it just contains information -which will be used at runtime to access A's code. - -In Windows, using an import library is sort of like using \samp{import -spam}; it gives you access to spam's names, but does not create a -separate copy. On \UNIX, linking with a library is more like -\samp{from spam import *}; it does create a separate copy. - - -\section{Using DLLs in Practice \label{win-dlls}} -\sectionauthor{Chris Phoenix}{cphoenix@best.com} - -Windows Python is built in Microsoft Visual \Cpp; using other -compilers may or may not work (though Borland seems to). The rest of -this section is MSV\Cpp{} specific. - -When creating DLLs in Windows, you must pass \file{pythonXY.lib} to -the linker. To build two DLLs, spam and ni (which uses C functions -found in spam), you could use these commands: - -\begin{verbatim} -cl /LD /I/python/include spam.c ../libs/pythonXY.lib -cl /LD /I/python/include ni.c spam.lib ../libs/pythonXY.lib -\end{verbatim} - -The first command created three files: \file{spam.obj}, -\file{spam.dll} and \file{spam.lib}. \file{Spam.dll} does not contain -any Python functions (such as \cfunction{PyArg_ParseTuple()}), but it -does know how to find the Python code thanks to \file{pythonXY.lib}. - -The second command created \file{ni.dll} (and \file{.obj} and -\file{.lib}), which knows how to find the necessary functions from -spam, and also from the Python executable. - -Not every identifier is exported to the lookup table. If you want any -other modules (including Python) to be able to see your identifiers, -you have to say \samp{_declspec(dllexport)}, as in \samp{void -_declspec(dllexport) initspam(void)} or \samp{PyObject -_declspec(dllexport) *NiGetSpamData(void)}. - -Developer Studio will throw in a lot of import libraries that you do -not really need, adding about 100K to your executable. To get rid of -them, use the Project Settings dialog, Link tab, to specify -\emph{ignore default libraries}. Add the correct -\file{msvcrt\var{xx}.lib} to the list of libraries. |