diff options
Diffstat (limited to 'Misc')
| -rw-r--r-- | Misc/FAQ | 240 |
1 files changed, 195 insertions, 45 deletions
@@ -3,14 +3,14 @@ Newsgroups: comp.lang.python,comp.answers,news.answers Followup-to: comp.lang.python From: guido@cwi.nl (Guido van Rossum) Reply-to: guido@cnri.reston.va.us (Guido van Rossum) -Expires: Fri, 1 Sep 1995 00:00:00 GMT +Expires: Sun, 1 Oct 1995 00:00:00 GMT Supersedes: <DCA29p.A9A@cwi.nl> Approved: news-answers-request@MIT.Edu Archive-name: python-faq/part1 Submitted-by: Guido van Rossum <guido@cwi.nl> -Version: 1.25++ -Last-modified: 25 July 1995 +Version: 1.27 +Last-modified: 28 August 1995 This article contains answers to Frequently Asked Questions about Python (an object-oriented interpreted programming language -- see @@ -21,13 +21,12 @@ redistribution of this FAQ is allowed. Printed redistribution only with permission of the author. No warranties. Author's address: - Guido van Rossum - CWI, dept. CST - Kruislaan 413 - P.O. Box 94079 - 1090 GB Amsterdam - The Netherlands -Email: <guido@cwi.nl> + Guido van Rossum + C.N.R.I. + 1895 Preston White Drive + Reston, VA 22091 + U.S.A. +Email: <guido@python.org>, <guido@cnri.reston.va.us>, <guido@cwi.nl> The latest version of this FAQ is available by anonymous ftp from <URL:ftp://ftp.python.org/pub/python/FAQ>. It will also be posted @@ -49,7 +48,7 @@ This FAQ is divided in the following chapters: 1. General information and availability 2. Python in the real world - 3. Building Python + 3. Building Python and Other Known Bugs 4. Programming in Python 5. Extending Python 6. Python's design @@ -89,8 +88,9 @@ Here's an overview of the questions per chapter: 2.5. Q. When will the next version be released? 2.6. Q. What new developments are expected for Python in the future? 2.7. Q. Is it reasonable to propose incompatible changes to Python? + 2.8. Q. What is the future of Python? - 3. Building Python + 3. Building Python and Other Known Bugs 3.1. Q. Is there a test set? 3.2. Q. When running the test set, I get complaints about floating point operations, but when playing with floating point operations I cannot @@ -110,6 +110,10 @@ Here's an overview of the questions per chapter: 3.13. Q. How to configure dynamic loading on Lixux. 3.14. Q. Under Solaris 2.x, using GCC, how do I use shared libraries? 3.15. Q. Errors when linking with a shared library containing C++ code. + 3.16. Q. Tk menus don't work properly in Python 1.2 + 3.17. Q. I built with tkintermodule.c enabled but get "Tkinter not found" + 3.18. Q. I built with Tk 4.0 but Tkinter complains about the Tk version + 3.19. Q. Tk doesn't work right on DEC Alpha 4. Programming in Python 4.1. Q. Is there a source code level debugger with breakpoints, step, @@ -176,10 +180,10 @@ Here's an overview of the questions per chapter: 5.8. Q. How do I call an object's method from C? 5.9. Q. How do I catch the output from print_error()? 5.10. Q. How do I access a module written in Python from C? + 5.11. Q. How do I interface to C++ objects from Python? 6. Python's design - 6.1. Q. Why isn't there a generic copying operation for objects in - Python? + 6.1. Q. Why isn't there a generic copying operation for objects in Python? 6.2. Q. Why isn't there a generic way to implement persistent objects in Python? (Persistent == automatically saved to and restored from disk.) @@ -199,6 +203,7 @@ Here's an overview of the questions per chapter: 6.11. Q. Why can't lambda forms contain statements? 6.12. Q. Why is there no more efficient way of iterating over a dictionary than first constructing the list of keys()? + 6.13. Q. Can Python be compiled to machine code, C or some other language? 7. Using Python on non-UNIX platforms 7.1. Q. Is there a Mac version of Python? @@ -225,7 +230,7 @@ question 4.2 in vi, type /^4\.2\. Q/). 1. General information and availability -======================================= + ======================================= 1.1. Q. What is Python? @@ -294,7 +299,7 @@ site). A. The following anonymous ftp sites keep mirrors of the Python distribution: - <URL:ftp://ftp.cwi.nl/pub/python/> + <URL:ftp://ftp.cwi.nl/pub/python/> <URL:ftp://gatekeeper.dec.com/pub/plan/python/> <URL:ftp://ftp.uu.net/languages/python/> <URL:ftp://ftp.wustl.edu/graphics/graphics/sgi-stuff/python/> @@ -302,7 +307,7 @@ distribution: <URL:ftp://ftp.sunet.se/pub/lang/python/> <URL:ftp://unix.hensa.ac.uk/mirrors/uunet/languages/python/> <URL:ftp://ftp.sterling.com/programming/languages/python/> - <URL:ftp://ftp.ibp.fr/pub/python/> + <URL:ftp://ftp.ibp.fr/pub/python/> <URL:ftp://ftp.switch.ch/software/sources/python/> <URL:ftp://ftp.informatik.tu-muenchen.de/pub/comp/programming/languages/python/> @@ -484,6 +489,10 @@ on the net since then. Missing-him-too-ly yours... +PS: support for Python's Emacs mode (Misc/python-mode.el in the +distribution) has been taken up by Barry Warsaw. Questions about it +should be mailed to <python-mode@python.org>. + 2. Python in the real world =========================== @@ -499,6 +508,9 @@ is even less meaningful. I see new names on the newsgroup all the time and my best guess is that there are currently at least several thousands of users. +Another statistic is the number of accesses to the Python WWW server. +Have a look at <URL:http://www.python.org/stats/>. + 2.2. Q. Have any significant projects been done in Python? A. Here at CWI (the home of Python), we have written a 20,000 line @@ -516,6 +528,8 @@ The University of California, Irvine uses a student administration system called TELE-Vision written entirely in Python. Contact: Ray Price <rlprice@uci.edu>. +See also the next question. + If you have done a significant project in Python that you'd like to be included in the list above, send me email! @@ -549,6 +563,13 @@ Individuals at many other companies are using Python for internal development or for as yet unannounced products (witness their contributions to the Python mailing list or newsgroup). +SGI has advertised in the Python list looking for Python programmers +for a project involving interactive television. + +See also the workshop minutes at +<URL:http://www.python.org/workshops/> -- in general the WWW server is +more up to date than the FAQ for these issues. + Python has also been elected as an extension language by MADE, a consortium supported by the European Committee's ESPRIT program and consisting of Bull, CWI and some other European companies. Contact: @@ -565,16 +586,17 @@ in the early stages of development, in fact new, stable releases 2.5. Q. When will the next version be released? -A. I am planning to release 1.3 in September or early October 1995. -It will contain keyword parameters as the most important new language -feature. Beta versions may be available as early as August. +A. I am planning to release 1.3 in early October 1995. It will +contain keyword parameters as the most important new language feature. +A beta version was made available in August, more beta versions may +appear. 2.6. Q. What new developments are expected for Python in the future? A. See my Work-In-Progress web page, currently at <URL:http://www.python.org:~guido/WIP.html>, and the pages for the Second Python Workshop (best reached via the Python home page, -<URL:http://www.python.org/>). +<URL:http://www.python.org/>). Also follow the newsgroup discussions! 2.7. Q. Is it reasonable to propose incompatible changes to Python? @@ -585,9 +607,28 @@ upon. Even if you can provide a conversion program, there still is the problem of updating all documentation. Providing a gradual upgrade path is the only way if a feature has to be changed. +2.8. Q. What is the future of Python? -3. Building Python -================== +A. If I knew, I'd be rich :-) + +Seriously, the formation of the PSA (Pyton Software Activity, see +<URL:http://www.python.org/psa/>) ensures some kind of support even in +the (unlikely! event that I'd be hit by a bus (actually, here in the +US, a car accident would be more likely :-), were to join a nunnery, +or would be head-hunted. A large number of Python users have become +experts at Python programming as well as maintenance of the +implementation, and would easily fill the vacuum created by my +disappearance. + +In the mean time, I have no plans to disappear -- rather, I am +committed to improving Python, and my current benefactor, CNRI (see +<URL:http://www.cnri.reston.va.us>) is just as committed to continue +its support of Python and the PSA. In fact, we have great plans for +Python -- we just can't tell yet! + + +3. Building Python and Other Known Bugs +======================================= 3.1. Q. Is there a test set? @@ -797,6 +838,42 @@ A. Link the main Python binary with C++. Change the definition of LINKCC in Modules/Makefile to be your C++ compiler. You may have to edit config.c slightly to make it compilable with C++. +3.16. Q. Tk menus don't work properly in Python 1.2. + +A. There's a bug in Tkinter.py; remove ClassType and InstanceType from +the definition of CallableTypes near the top of Lib/tkinter/Tkinter.py. + +3.17. Q. I built with tkintermodule.c enabled but get "Tkinter not found". + +A. Tkinter.py (note: upper case T) lives in a subdirectory of Lib, +Lib/tkinter. If you are using the default module search path, you +probably didn't enable the line in the Modules/Setup file defining +TKPATH; if you use the environment variable PYTHONPATH, you'll have to +add the proper tkinter subdirectory. + +3.18. Q. I built with Tk 4.0 but Tkinter complains about the Tk version. + +A. Several things could cause this. You most likely have a Tk 3.6 +installation that wasn't completely eradicated by the Tk 4.0 +installation (which tends to add "4.0" to its installed files). You +may have the Tk 3.6 support library installed in the place where the +Tk 4.0 support files should be (default /usr/local/lib/tk/); you may +have compiled Python with the old tk.h header file (yes, this actually +compiles!); you may actually have linked with Tk 3.6 even though Tk +4.0 is also around. Similar for Tcl 7.4 vs. Tcl 7.3. + +3.19. Q. Tk doesn't work right on DEC Alpha. + +A. You probably compiled either Tcl, Tk or Python with gcc. Don't. +For this platform, which has 64-bit integers, gcc is known to generate +broken code. The standard cc (which comes bundled with the OS!) +works. If you still prefer gcc, at least try recompiling with cc +before reporting problems to the newsgroup or the author; if this +fixes the problem, report the bug to the gcc developers instead. (As +far as we know, there are no problem with gcc on other platforms -- +the instabilities seem to be restricted to the DEC Alpha.) See also +question 3.6. + 4. Programming in Python ======================== @@ -1598,33 +1675,59 @@ the module) as follows: Calling setattr(), to assign to variables in the module, also works. +5.11. Q. How do I interface to C++ objects from Python? + +A. Depending on your requirements, there are many approaches. Begin +by reading the "Extending and Embedding" document (Doc/ext.tex, see +also <URL:http://www.python.org/doc/>). Realize that for the Python +run-time system, there isn't a whole lot of difference between C and +C++ -- so the strategy to build a new Python type around a C structure +(pointer) type will also work for C++ objects. + +Automatic generation of interfaces between Python and C++ is still at +the horizon -- parsing C++ header files requires an almost complete +C++ parser, and many features aren't easily translated from C++ to +Python: certain forms of operator oveloading, function overloading +(best approached by a varargs function which explicitly type-checks +its arguments), and reference arguments are just a number of features +that are hard to translate correctly if at all. + +The hardest problem is to transparently translate the C++ class +hierarchy to Python, so that Python programs derive classes from C++ +classes. Given suitable constraints, this may be possible, but it +would require more space than I have in this FAQ to explain how. +In any case, you can get quite a bit done without this, using just the +existing classes from Python. + +If this all seems rather daunting, that may be because it is -- C++ +isn't exactly a baby to handle without gloves! However, people have +accomplished amazing feats of interfacing between Python and C++, and +a detailed question posted to the Python list is likely to elicit some +interesting and useful responses. + 6. Python's design ================== -6.1. Q. Why isn't there a generic copying operation for objects in -Python? +6.1. Q. Why isn't there a generic copying operation for objects in Python? -A. Hmm. Maybe there should be one, but it's difficult to assign a -useful meaning to copying of open files, sockets and windows, or -recursive data structures. As long as you design all your classes -yourself you are of course free to define a standard base class that -defines an overridable copying operation for all the objects you care -about. (One practical point: it would have to be a built-in function, -not a standard method name, since not all built-in object types have -methods; e.g. strings, integers and tuples don't.) +A. Historically, there wasn't. However, starting in Python 1.2, +there's a library module "copy" which supports both shallow and deep +copying of most common Python objects (though not things like open +files, sockets or windows), including an extensible mechanism to copy +class instances. 6.2. Q. Why isn't there a generic way to implement persistent objects in Python? (Persistent == automatically saved to and restored from disk.) -A. Hmm, hmm. Basically for the same reasons as why there is no -generic copying operation. - -A partial solution will appear in release 1.2. This will also provide -a partial solution to the problem of a generic copying operation. -(Partial because it still won't cope with open files etc.; however it -does handle user-defined classes!) +A. Like the previous question, historically, there wasn't. The +library module "pickle" now solves this in a very general way (though +you still can't store things like open files, sockests or windows), +and the library module "shelve" uses pickle and (g)dbm to create +presistent mappings containing arbitrary Python objects. There are +some problems with shelve when using gdbm which will be solved in +Python 1.3. 6.3. Q. Why isn't there a switch or case statement in Python? @@ -1810,6 +1913,52 @@ programs: it's easy never to have it happen during test runs if you only insert or delete a few items per iteration -- but your users will surely hit upon it sooner or later. +6.13. Q. Can Python be compiled to machine code, C or some other language? + +A. Not easily. Python's high level data types, dynamic typing of +objects and run-time invocation of the interpreter (using eval() or +exec) together mean that a "compiled" Python program would probably +consist mostly of calls into the Python run-time system, even for +seemingly simple operations like "x+1". Thus, the performance gain +would probably be minimal. + +Internally, Python source code is always translated into a "virtual +machine code" or "byte code" representation before it is interpreted +(by the "Python virtual machine" or "bytecode interpreter"). In order +to avoid the overhead of parsing and translating modules that rarely +change over and over again, this byte code is written on a file whose +name ends in ".pyc" whenever a module is parsed (from a file whose +name ends in ".py"). When the corresponding .py file is changed, it +is parsed and translated again and the .pyc file is rewritten. There +is no performance difference once the .pyc file has been loaded (the +bytecode read from the .pyc file is exactly the same as the bytecode +created by direct translation). The only difference is that loading +code from a .pyc file is faster than parsing and translating a .py +file, so the presence of precompiled .pyc files will generally improve +start-up time of Python scripts. If desired, the Lib/compileall.py +module/script can be used to force creation of valid .pyc files for a +given set of modules. + +If you are looking for a way to translate Python programs in order to +distribute them in binary form, without the need to distribute the +interpreter and library as well, have a look at the freeze.py script +in the Tools/freeze directory. This creates a single binary file +incorporating your program, the Python interpreter, and those parts of +the Python library that are needed by your program. Of course, the +resulting binary will only run on the same type of platform as that +used to create it. + +Hints for proper usage of freeze.py: + +- the script must be in a file whose name ends in .py + +- you must have installed Python fully: + + make install + make libinstall + make inclinstall + make libainstall + 7. Using Python on non-UNIX platforms ===================================== @@ -1872,11 +2021,12 @@ else is working on a more complete port, for details watch the list. 7.8. Q. What about IBM mainframes, or other non-UNIX platforms? -A. I haven't heard about these, except I remember once hearing about -an attempt at an OS/9 port. If you're interested in any of this, go -directly to the newsgroup and ask there, you may find exactly what you -need. For example, a port to MPE/iX 5.0 on HP3000 computers was just -announced, see <URL:http://www.allegro.com/software/>. +A. I haven't heard about these, except I remember hearing about an +OS/9 port and a port to Vxworks (both operating systems for embedded +systems). If you're interested in any of this, go directly to the +newsgroup and ask there, you may find exactly what you need. For +example, a port to MPE/iX 5.0 on HP3000 computers was just announced, +see <URL:http://www.allegro.com/software/>. 7.9. Q. Where are the source or Makefiles for the non-UNIX versions? |