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author | Georg Brandl <georg@python.org> | 2007-08-15 14:28:01 (GMT) |
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committer | Georg Brandl <georg@python.org> | 2007-08-15 14:28:01 (GMT) |
commit | 8ec7f656134b1230ab23003a94ba3266d7064122 (patch) | |
tree | bc730d5fb3302dc375edd26b26f750d609b61d72 /Doc/library/inspect.rst | |
parent | f56181ff53ba00b7bed3997a4dccd9a1b6217b57 (diff) | |
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Move the 2.6 reST doc tree in place.
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diff --git a/Doc/library/inspect.rst b/Doc/library/inspect.rst new file mode 100644 index 0000000..04ea977 --- /dev/null +++ b/Doc/library/inspect.rst @@ -0,0 +1,511 @@ + +:mod:`inspect` --- Inspect live objects +======================================= + +.. module:: inspect + :synopsis: Extract information and source code from live objects. +.. moduleauthor:: Ka-Ping Yee <ping@lfw.org> +.. sectionauthor:: Ka-Ping Yee <ping@lfw.org> + + +.. versionadded:: 2.1 + +The :mod:`inspect` module provides several useful functions to help get +information about live objects such as modules, classes, methods, functions, +tracebacks, frame objects, and code objects. For example, it can help you +examine the contents of a class, retrieve the source code of a method, extract +and format the argument list for a function, or get all the information you need +to display a detailed traceback. + +There are four main kinds of services provided by this module: type checking, +getting source code, inspecting classes and functions, and examining the +interpreter stack. + + +.. _inspect-types: + +Types and members +----------------- + +The :func:`getmembers` function retrieves the members of an object such as a +class or module. The eleven functions whose names begin with "is" are mainly +provided as convenient choices for the second argument to :func:`getmembers`. +They also help you determine when you can expect to find the following special +attributes: + ++-----------+-----------------+---------------------------+-------+ +| Type | Attribute | Description | Notes | ++===========+=================+===========================+=======+ +| module | __doc__ | documentation string | | ++-----------+-----------------+---------------------------+-------+ +| | __file__ | filename (missing for | | +| | | built-in modules) | | ++-----------+-----------------+---------------------------+-------+ +| class | __doc__ | documentation string | | ++-----------+-----------------+---------------------------+-------+ +| | __module__ | name of module in which | | +| | | this class was defined | | ++-----------+-----------------+---------------------------+-------+ +| method | __doc__ | documentation string | | ++-----------+-----------------+---------------------------+-------+ +| | __name__ | name with which this | | +| | | method was defined | | ++-----------+-----------------+---------------------------+-------+ +| | im_class | class object that asked | \(1) | +| | | for this method | | ++-----------+-----------------+---------------------------+-------+ +| | im_func | function object | | +| | | containing implementation | | +| | | of method | | ++-----------+-----------------+---------------------------+-------+ +| | im_self | instance to which this | | +| | | method is bound, or | | +| | | ``None`` | | ++-----------+-----------------+---------------------------+-------+ +| function | __doc__ | documentation string | | ++-----------+-----------------+---------------------------+-------+ +| | __name__ | name with which this | | +| | | function was defined | | ++-----------+-----------------+---------------------------+-------+ +| | func_code | code object containing | | +| | | compiled function | | +| | | bytecode | | ++-----------+-----------------+---------------------------+-------+ +| | func_defaults | tuple of any default | | +| | | values for arguments | | ++-----------+-----------------+---------------------------+-------+ +| | func_doc | (same as __doc__) | | ++-----------+-----------------+---------------------------+-------+ +| | func_globals | global namespace in which | | +| | | this function was defined | | ++-----------+-----------------+---------------------------+-------+ +| | func_name | (same as __name__) | | ++-----------+-----------------+---------------------------+-------+ +| traceback | tb_frame | frame object at this | | +| | | level | | ++-----------+-----------------+---------------------------+-------+ +| | tb_lasti | index of last attempted | | +| | | instruction in bytecode | | ++-----------+-----------------+---------------------------+-------+ +| | tb_lineno | current line number in | | +| | | Python source code | | ++-----------+-----------------+---------------------------+-------+ +| | tb_next | next inner traceback | | +| | | object (called by this | | +| | | level) | | ++-----------+-----------------+---------------------------+-------+ +| frame | f_back | next outer frame object | | +| | | (this frame's caller) | | ++-----------+-----------------+---------------------------+-------+ +| | f_builtins | built-in namespace seen | | +| | | by this frame | | ++-----------+-----------------+---------------------------+-------+ +| | f_code | code object being | | +| | | executed in this frame | | ++-----------+-----------------+---------------------------+-------+ +| | f_exc_traceback | traceback if raised in | | +| | | this frame, or ``None`` | | ++-----------+-----------------+---------------------------+-------+ +| | f_exc_type | exception type if raised | | +| | | in this frame, or | | +| | | ``None`` | | ++-----------+-----------------+---------------------------+-------+ +| | f_exc_value | exception value if raised | | +| | | in this frame, or | | +| | | ``None`` | | ++-----------+-----------------+---------------------------+-------+ +| | f_globals | global namespace seen by | | +| | | this frame | | ++-----------+-----------------+---------------------------+-------+ +| | f_lasti | index of last attempted | | +| | | instruction in bytecode | | ++-----------+-----------------+---------------------------+-------+ +| | f_lineno | current line number in | | +| | | Python source code | | ++-----------+-----------------+---------------------------+-------+ +| | f_locals | local namespace seen by | | +| | | this frame | | ++-----------+-----------------+---------------------------+-------+ +| | f_restricted | 0 or 1 if frame is in | | +| | | restricted execution mode | | ++-----------+-----------------+---------------------------+-------+ +| | f_trace | tracing function for this | | +| | | frame, or ``None`` | | ++-----------+-----------------+---------------------------+-------+ +| code | co_argcount | number of arguments (not | | +| | | including \* or \*\* | | +| | | args) | | ++-----------+-----------------+---------------------------+-------+ +| | co_code | string of raw compiled | | +| | | bytecode | | ++-----------+-----------------+---------------------------+-------+ +| | co_consts | tuple of constants used | | +| | | in the bytecode | | ++-----------+-----------------+---------------------------+-------+ +| | co_filename | name of file in which | | +| | | this code object was | | +| | | created | | ++-----------+-----------------+---------------------------+-------+ +| | co_firstlineno | number of first line in | | +| | | Python source code | | ++-----------+-----------------+---------------------------+-------+ +| | co_flags | bitmap: 1=optimized ``|`` | | +| | | 2=newlocals ``|`` 4=\*arg | | +| | | ``|`` 8=\*\*arg | | ++-----------+-----------------+---------------------------+-------+ +| | co_lnotab | encoded mapping of line | | +| | | numbers to bytecode | | +| | | indices | | ++-----------+-----------------+---------------------------+-------+ +| | co_name | name with which this code | | +| | | object was defined | | ++-----------+-----------------+---------------------------+-------+ +| | co_names | tuple of names of local | | +| | | variables | | ++-----------+-----------------+---------------------------+-------+ +| | co_nlocals | number of local variables | | ++-----------+-----------------+---------------------------+-------+ +| | co_stacksize | virtual machine stack | | +| | | space required | | ++-----------+-----------------+---------------------------+-------+ +| | co_varnames | tuple of names of | | +| | | arguments and local | | +| | | variables | | ++-----------+-----------------+---------------------------+-------+ +| builtin | __doc__ | documentation string | | ++-----------+-----------------+---------------------------+-------+ +| | __name__ | original name of this | | +| | | function or method | | ++-----------+-----------------+---------------------------+-------+ +| | __self__ | instance to which a | | +| | | method is bound, or | | +| | | ``None`` | | ++-----------+-----------------+---------------------------+-------+ + +Note: + +(1) + .. versionchanged:: 2.2 + :attr:`im_class` used to refer to the class that defined the method. + + +.. function:: getmembers(object[, predicate]) + + Return all the members of an object in a list of (name, value) pairs sorted by + name. If the optional *predicate* argument is supplied, only members for which + the predicate returns a true value are included. + + +.. function:: getmoduleinfo(path) + + Return a tuple of values that describe how Python will interpret the file + identified by *path* if it is a module, or ``None`` if it would not be + identified as a module. The return tuple is ``(name, suffix, mode, mtype)``, + where *name* is the name of the module without the name of any enclosing + package, *suffix* is the trailing part of the file name (which may not be a + dot-delimited extension), *mode* is the :func:`open` mode that would be used + (``'r'`` or ``'rb'``), and *mtype* is an integer giving the type of the + module. *mtype* will have a value which can be compared to the constants + defined in the :mod:`imp` module; see the documentation for that module for + more information on module types. + + +.. function:: getmodulename(path) + + Return the name of the module named by the file *path*, without including the + names of enclosing packages. This uses the same algorithm as the interpreter + uses when searching for modules. If the name cannot be matched according to the + interpreter's rules, ``None`` is returned. + + +.. function:: ismodule(object) + + Return true if the object is a module. + + +.. function:: isclass(object) + + Return true if the object is a class. + + +.. function:: ismethod(object) + + Return true if the object is a method. + + +.. function:: isfunction(object) + + Return true if the object is a Python function or unnamed (lambda) function. + + +.. function:: istraceback(object) + + Return true if the object is a traceback. + + +.. function:: isframe(object) + + Return true if the object is a frame. + + +.. function:: iscode(object) + + Return true if the object is a code. + + +.. function:: isbuiltin(object) + + Return true if the object is a built-in function. + + +.. function:: isroutine(object) + + Return true if the object is a user-defined or built-in function or method. + + +.. function:: ismethoddescriptor(object) + + Return true if the object is a method descriptor, but not if ismethod() or + isclass() or isfunction() are true. + + This is new as of Python 2.2, and, for example, is true of int.__add__. An + object passing this test has a __get__ attribute but not a __set__ attribute, + but beyond that the set of attributes varies. __name__ is usually sensible, and + __doc__ often is. + + Methods implemented via descriptors that also pass one of the other tests return + false from the ismethoddescriptor() test, simply because the other tests promise + more -- you can, e.g., count on having the im_func attribute (etc) when an + object passes ismethod(). + + +.. function:: isdatadescriptor(object) + + Return true if the object is a data descriptor. + + Data descriptors have both a __get__ and a __set__ attribute. Examples are + properties (defined in Python), getsets, and members. The latter two are + defined in C and there are more specific tests available for those types, which + is robust across Python implementations. Typically, data descriptors will also + have __name__ and __doc__ attributes (properties, getsets, and members have both + of these attributes), but this is not guaranteed. + + .. versionadded:: 2.3 + + +.. function:: isgetsetdescriptor(object) + + Return true if the object is a getset descriptor. + + getsets are attributes defined in extension modules via ``PyGetSetDef`` + structures. For Python implementations without such types, this method will + always return ``False``. + + .. versionadded:: 2.5 + + +.. function:: ismemberdescriptor(object) + + Return true if the object is a member descriptor. + + Member descriptors are attributes defined in extension modules via + ``PyMemberDef`` structures. For Python implementations without such types, this + method will always return ``False``. + + .. versionadded:: 2.5 + + +.. _inspect-source: + +Retrieving source code +---------------------- + + +.. function:: getdoc(object) + + Get the documentation string for an object. All tabs are expanded to spaces. To + clean up docstrings that are indented to line up with blocks of code, any + whitespace than can be uniformly removed from the second line onwards is + removed. + + +.. function:: getcomments(object) + + Return in a single string any lines of comments immediately preceding the + object's source code (for a class, function, or method), or at the top of the + Python source file (if the object is a module). + + +.. function:: getfile(object) + + Return the name of the (text or binary) file in which an object was defined. + This will fail with a :exc:`TypeError` if the object is a built-in module, + class, or function. + + +.. function:: getmodule(object) + + Try to guess which module an object was defined in. + + +.. function:: getsourcefile(object) + + Return the name of the Python source file in which an object was defined. This + will fail with a :exc:`TypeError` if the object is a built-in module, class, or + function. + + +.. function:: getsourcelines(object) + + Return a list of source lines and starting line number for an object. The + argument may be a module, class, method, function, traceback, frame, or code + object. The source code is returned as a list of the lines corresponding to the + object and the line number indicates where in the original source file the first + line of code was found. An :exc:`IOError` is raised if the source code cannot + be retrieved. + + +.. function:: getsource(object) + + Return the text of the source code for an object. The argument may be a module, + class, method, function, traceback, frame, or code object. The source code is + returned as a single string. An :exc:`IOError` is raised if the source code + cannot be retrieved. + + +.. _inspect-classes-functions: + +Classes and functions +--------------------- + + +.. function:: getclasstree(classes[, unique]) + + Arrange the given list of classes into a hierarchy of nested lists. Where a + nested list appears, it contains classes derived from the class whose entry + immediately precedes the list. Each entry is a 2-tuple containing a class and a + tuple of its base classes. If the *unique* argument is true, exactly one entry + appears in the returned structure for each class in the given list. Otherwise, + classes using multiple inheritance and their descendants will appear multiple + times. + + +.. function:: getargspec(func) + + Get the names and default values of a function's arguments. A tuple of four + things is returned: ``(args, varargs, varkw, defaults)``. *args* is a list of + the argument names (it may contain nested lists). *varargs* and *varkw* are the + names of the ``*`` and ``**`` arguments or ``None``. *defaults* is a tuple of + default argument values or None if there are no default arguments; if this tuple + has *n* elements, they correspond to the last *n* elements listed in *args*. + + +.. function:: getargvalues(frame) + + Get information about arguments passed into a particular frame. A tuple of four + things is returned: ``(args, varargs, varkw, locals)``. *args* is a list of the + argument names (it may contain nested lists). *varargs* and *varkw* are the + names of the ``*`` and ``**`` arguments or ``None``. *locals* is the locals + dictionary of the given frame. + + +.. function:: formatargspec(args[, varargs, varkw, defaults, formatarg, formatvarargs, formatvarkw, formatvalue, join]) + + Format a pretty argument spec from the four values returned by + :func:`getargspec`. The format\* arguments are the corresponding optional + formatting functions that are called to turn names and values into strings. + + +.. function:: formatargvalues(args[, varargs, varkw, locals, formatarg, formatvarargs, formatvarkw, formatvalue, join]) + + Format a pretty argument spec from the four values returned by + :func:`getargvalues`. The format\* arguments are the corresponding optional + formatting functions that are called to turn names and values into strings. + + +.. function:: getmro(cls) + + Return a tuple of class cls's base classes, including cls, in method resolution + order. No class appears more than once in this tuple. Note that the method + resolution order depends on cls's type. Unless a very peculiar user-defined + metatype is in use, cls will be the first element of the tuple. + + +.. _inspect-stack: + +The interpreter stack +--------------------- + +When the following functions return "frame records," each record is a tuple of +six items: the frame object, the filename, the line number of the current line, +the function name, a list of lines of context from the source code, and the +index of the current line within that list. + +.. warning:: + + Keeping references to frame objects, as found in the first element of the frame + records these functions return, can cause your program to create reference + cycles. Once a reference cycle has been created, the lifespan of all objects + which can be accessed from the objects which form the cycle can become much + longer even if Python's optional cycle detector is enabled. If such cycles must + be created, it is important to ensure they are explicitly broken to avoid the + delayed destruction of objects and increased memory consumption which occurs. + + Though the cycle detector will catch these, destruction of the frames (and local + variables) can be made deterministic by removing the cycle in a + :keyword:`finally` clause. This is also important if the cycle detector was + disabled when Python was compiled or using :func:`gc.disable`. For example:: + + def handle_stackframe_without_leak(): + frame = inspect.currentframe() + try: + # do something with the frame + finally: + del frame + +The optional *context* argument supported by most of these functions specifies +the number of lines of context to return, which are centered around the current +line. + + +.. function:: getframeinfo(frame[, context]) + + Get information about a frame or traceback object. A 5-tuple is returned, the + last five elements of the frame's frame record. + + +.. function:: getouterframes(frame[, context]) + + Get a list of frame records for a frame and all outer frames. These frames + represent the calls that lead to the creation of *frame*. The first entry in the + returned list represents *frame*; the last entry represents the outermost call + on *frame*'s stack. + + +.. function:: getinnerframes(traceback[, context]) + + Get a list of frame records for a traceback's frame and all inner frames. These + frames represent calls made as a consequence of *frame*. The first entry in the + list represents *traceback*; the last entry represents where the exception was + raised. + + +.. function:: currentframe() + + Return the frame object for the caller's stack frame. + + +.. function:: stack([context]) + + Return a list of frame records for the caller's stack. The first entry in the + returned list represents the caller; the last entry represents the outermost + call on the stack. + + +.. function:: trace([context]) + + Return a list of frame records for the stack between the current frame and the + frame in which an exception currently being handled was raised in. The first + entry in the list represents the caller; the last entry represents where the + exception was raised. + |