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Georg Brandl116aa622007-08-15 14:28:22 +00001
2:mod:`inspect` --- Inspect live objects
3=======================================
4
5.. module:: inspect
6 :synopsis: Extract information and source code from live objects.
7.. moduleauthor:: Ka-Ping Yee <ping@lfw.org>
8.. sectionauthor:: Ka-Ping Yee <ping@lfw.org>
9
10
Georg Brandl116aa622007-08-15 14:28:22 +000011The :mod:`inspect` module provides several useful functions to help get
12information about live objects such as modules, classes, methods, functions,
13tracebacks, frame objects, and code objects. For example, it can help you
14examine the contents of a class, retrieve the source code of a method, extract
15and format the argument list for a function, or get all the information you need
16to display a detailed traceback.
17
18There are four main kinds of services provided by this module: type checking,
19getting source code, inspecting classes and functions, and examining the
20interpreter stack.
21
22
23.. _inspect-types:
24
25Types and members
26-----------------
27
28The :func:`getmembers` function retrieves the members of an object such as a
29class or module. The eleven functions whose names begin with "is" are mainly
30provided as convenient choices for the second argument to :func:`getmembers`.
31They also help you determine when you can expect to find the following special
32attributes:
33
Georg Brandl55ac8f02007-09-01 13:51:09 +000034+-----------+-----------------+---------------------------+
35| Type | Attribute | Description |
36+===========+=================+===========================+
37| module | __doc__ | documentation string |
38+-----------+-----------------+---------------------------+
39| | __file__ | filename (missing for |
40| | | built-in modules) |
41+-----------+-----------------+---------------------------+
42| class | __doc__ | documentation string |
43+-----------+-----------------+---------------------------+
44| | __module__ | name of module in which |
45| | | this class was defined |
46+-----------+-----------------+---------------------------+
47| method | __doc__ | documentation string |
48+-----------+-----------------+---------------------------+
49| | __name__ | name with which this |
50| | | method was defined |
51+-----------+-----------------+---------------------------+
52| | im_class | class object that asked |
53| | | for this method |
54+-----------+-----------------+---------------------------+
55| | im_func | function object |
56| | | containing implementation |
57| | | of method |
58+-----------+-----------------+---------------------------+
59| | im_self | instance to which this |
60| | | method is bound, or |
61| | | ``None`` |
62+-----------+-----------------+---------------------------+
63| function | __doc__ | documentation string |
64+-----------+-----------------+---------------------------+
65| | __name__ | name with which this |
66| | | function was defined |
67+-----------+-----------------+---------------------------+
68| | __code__ | code object containing |
69| | | compiled function |
70| | | bytecode |
71+-----------+-----------------+---------------------------+
72| | __defaults__ | tuple of any default |
73| | | values for arguments |
74+-----------+-----------------+---------------------------+
75| | __globals__ | global namespace in which |
76| | | this function was defined |
77+-----------+-----------------+---------------------------+
78| traceback | tb_frame | frame object at this |
79| | | level |
80+-----------+-----------------+---------------------------+
81| | tb_lasti | index of last attempted |
82| | | instruction in bytecode |
83+-----------+-----------------+---------------------------+
84| | tb_lineno | current line number in |
85| | | Python source code |
86+-----------+-----------------+---------------------------+
87| | tb_next | next inner traceback |
88| | | object (called by this |
89| | | level) |
90+-----------+-----------------+---------------------------+
91| frame | f_back | next outer frame object |
92| | | (this frame's caller) |
93+-----------+-----------------+---------------------------+
94| | f_builtins | built-in namespace seen |
95| | | by this frame |
96+-----------+-----------------+---------------------------+
97| | f_code | code object being |
98| | | executed in this frame |
99+-----------+-----------------+---------------------------+
100| | f_exc_traceback | traceback if raised in |
101| | | this frame, or ``None`` |
102+-----------+-----------------+---------------------------+
103| | f_exc_type | exception type if raised |
104| | | in this frame, or |
105| | | ``None`` |
106+-----------+-----------------+---------------------------+
107| | f_exc_value | exception value if raised |
108| | | in this frame, or |
109| | | ``None`` |
110+-----------+-----------------+---------------------------+
111| | f_globals | global namespace seen by |
112| | | this frame |
113+-----------+-----------------+---------------------------+
114| | f_lasti | index of last attempted |
115| | | instruction in bytecode |
116+-----------+-----------------+---------------------------+
117| | f_lineno | current line number in |
118| | | Python source code |
119+-----------+-----------------+---------------------------+
120| | f_locals | local namespace seen by |
121| | | this frame |
122+-----------+-----------------+---------------------------+
123| | f_restricted | 0 or 1 if frame is in |
124| | | restricted execution mode |
125+-----------+-----------------+---------------------------+
126| | f_trace | tracing function for this |
127| | | frame, or ``None`` |
128+-----------+-----------------+---------------------------+
129| code | co_argcount | number of arguments (not |
130| | | including \* or \*\* |
131| | | args) |
132+-----------+-----------------+---------------------------+
133| | co_code | string of raw compiled |
134| | | bytecode |
135+-----------+-----------------+---------------------------+
136| | co_consts | tuple of constants used |
137| | | in the bytecode |
138+-----------+-----------------+---------------------------+
139| | co_filename | name of file in which |
140| | | this code object was |
141| | | created |
142+-----------+-----------------+---------------------------+
143| | co_firstlineno | number of first line in |
144| | | Python source code |
145+-----------+-----------------+---------------------------+
146| | co_flags | bitmap: 1=optimized ``|`` |
147| | | 2=newlocals ``|`` 4=\*arg |
148| | | ``|`` 8=\*\*arg |
149+-----------+-----------------+---------------------------+
150| | co_lnotab | encoded mapping of line |
151| | | numbers to bytecode |
152| | | indices |
153+-----------+-----------------+---------------------------+
154| | co_name | name with which this code |
155| | | object was defined |
156+-----------+-----------------+---------------------------+
157| | co_names | tuple of names of local |
158| | | variables |
159+-----------+-----------------+---------------------------+
160| | co_nlocals | number of local variables |
161+-----------+-----------------+---------------------------+
162| | co_stacksize | virtual machine stack |
163| | | space required |
164+-----------+-----------------+---------------------------+
165| | co_varnames | tuple of names of |
166| | | arguments and local |
167| | | variables |
168+-----------+-----------------+---------------------------+
169| builtin | __doc__ | documentation string |
170+-----------+-----------------+---------------------------+
171| | __name__ | original name of this |
172| | | function or method |
173+-----------+-----------------+---------------------------+
174| | __self__ | instance to which a |
175| | | method is bound, or |
176| | | ``None`` |
177+-----------+-----------------+---------------------------+
Georg Brandl116aa622007-08-15 14:28:22 +0000178
179
180.. function:: getmembers(object[, predicate])
181
182 Return all the members of an object in a list of (name, value) pairs sorted by
183 name. If the optional *predicate* argument is supplied, only members for which
184 the predicate returns a true value are included.
185
186
187.. function:: getmoduleinfo(path)
188
189 Return a tuple of values that describe how Python will interpret the file
190 identified by *path* if it is a module, or ``None`` if it would not be
191 identified as a module. The return tuple is ``(name, suffix, mode, mtype)``,
192 where *name* is the name of the module without the name of any enclosing
193 package, *suffix* is the trailing part of the file name (which may not be a
194 dot-delimited extension), *mode* is the :func:`open` mode that would be used
195 (``'r'`` or ``'rb'``), and *mtype* is an integer giving the type of the
196 module. *mtype* will have a value which can be compared to the constants
197 defined in the :mod:`imp` module; see the documentation for that module for
198 more information on module types.
199
200
201.. function:: getmodulename(path)
202
203 Return the name of the module named by the file *path*, without including the
204 names of enclosing packages. This uses the same algorithm as the interpreter
205 uses when searching for modules. If the name cannot be matched according to the
206 interpreter's rules, ``None`` is returned.
207
208
209.. function:: ismodule(object)
210
211 Return true if the object is a module.
212
213
214.. function:: isclass(object)
215
216 Return true if the object is a class.
217
218
219.. function:: ismethod(object)
220
221 Return true if the object is a method.
222
223
224.. function:: isfunction(object)
225
226 Return true if the object is a Python function or unnamed (lambda) function.
227
228
229.. function:: istraceback(object)
230
231 Return true if the object is a traceback.
232
233
234.. function:: isframe(object)
235
236 Return true if the object is a frame.
237
238
239.. function:: iscode(object)
240
241 Return true if the object is a code.
242
243
244.. function:: isbuiltin(object)
245
246 Return true if the object is a built-in function.
247
248
249.. function:: isroutine(object)
250
251 Return true if the object is a user-defined or built-in function or method.
252
253
254.. function:: ismethoddescriptor(object)
255
256 Return true if the object is a method descriptor, but not if ismethod() or
257 isclass() or isfunction() are true.
258
259 This is new as of Python 2.2, and, for example, is true of int.__add__. An
260 object passing this test has a __get__ attribute but not a __set__ attribute,
261 but beyond that the set of attributes varies. __name__ is usually sensible, and
262 __doc__ often is.
263
264 Methods implemented via descriptors that also pass one of the other tests return
265 false from the ismethoddescriptor() test, simply because the other tests promise
266 more -- you can, e.g., count on having the im_func attribute (etc) when an
267 object passes ismethod().
268
269
270.. function:: isdatadescriptor(object)
271
272 Return true if the object is a data descriptor.
273
274 Data descriptors have both a __get__ and a __set__ attribute. Examples are
275 properties (defined in Python), getsets, and members. The latter two are
276 defined in C and there are more specific tests available for those types, which
277 is robust across Python implementations. Typically, data descriptors will also
278 have __name__ and __doc__ attributes (properties, getsets, and members have both
279 of these attributes), but this is not guaranteed.
280
Georg Brandl116aa622007-08-15 14:28:22 +0000281
282.. function:: isgetsetdescriptor(object)
283
284 Return true if the object is a getset descriptor.
285
286 getsets are attributes defined in extension modules via ``PyGetSetDef``
287 structures. For Python implementations without such types, this method will
288 always return ``False``.
289
Georg Brandl116aa622007-08-15 14:28:22 +0000290
291.. function:: ismemberdescriptor(object)
292
293 Return true if the object is a member descriptor.
294
295 Member descriptors are attributes defined in extension modules via
296 ``PyMemberDef`` structures. For Python implementations without such types, this
297 method will always return ``False``.
298
Georg Brandl116aa622007-08-15 14:28:22 +0000299
300.. _inspect-source:
301
302Retrieving source code
303----------------------
304
305
306.. function:: getdoc(object)
307
308 Get the documentation string for an object. All tabs are expanded to spaces. To
309 clean up docstrings that are indented to line up with blocks of code, any
310 whitespace than can be uniformly removed from the second line onwards is
311 removed.
312
313
314.. function:: getcomments(object)
315
316 Return in a single string any lines of comments immediately preceding the
317 object's source code (for a class, function, or method), or at the top of the
318 Python source file (if the object is a module).
319
320
321.. function:: getfile(object)
322
323 Return the name of the (text or binary) file in which an object was defined.
324 This will fail with a :exc:`TypeError` if the object is a built-in module,
325 class, or function.
326
327
328.. function:: getmodule(object)
329
330 Try to guess which module an object was defined in.
331
332
333.. function:: getsourcefile(object)
334
335 Return the name of the Python source file in which an object was defined. This
336 will fail with a :exc:`TypeError` if the object is a built-in module, class, or
337 function.
338
339
340.. function:: getsourcelines(object)
341
342 Return a list of source lines and starting line number for an object. The
343 argument may be a module, class, method, function, traceback, frame, or code
344 object. The source code is returned as a list of the lines corresponding to the
345 object and the line number indicates where in the original source file the first
346 line of code was found. An :exc:`IOError` is raised if the source code cannot
347 be retrieved.
348
349
350.. function:: getsource(object)
351
352 Return the text of the source code for an object. The argument may be a module,
353 class, method, function, traceback, frame, or code object. The source code is
354 returned as a single string. An :exc:`IOError` is raised if the source code
355 cannot be retrieved.
356
357
358.. _inspect-classes-functions:
359
360Classes and functions
361---------------------
362
363
364.. function:: getclasstree(classes[, unique])
365
366 Arrange the given list of classes into a hierarchy of nested lists. Where a
367 nested list appears, it contains classes derived from the class whose entry
368 immediately precedes the list. Each entry is a 2-tuple containing a class and a
369 tuple of its base classes. If the *unique* argument is true, exactly one entry
370 appears in the returned structure for each class in the given list. Otherwise,
371 classes using multiple inheritance and their descendants will appear multiple
372 times.
373
374
375.. function:: getargspec(func)
376
377 Get the names and default values of a function's arguments. A tuple of four
378 things is returned: ``(args, varargs, varkw, defaults)``. *args* is a list of
379 the argument names (it may contain nested lists). *varargs* and *varkw* are the
380 names of the ``*`` and ``**`` arguments or ``None``. *defaults* is a tuple of
381 default argument values or None if there are no default arguments; if this tuple
382 has *n* elements, they correspond to the last *n* elements listed in *args*.
383
384
385.. function:: getargvalues(frame)
386
387 Get information about arguments passed into a particular frame. A tuple of four
388 things is returned: ``(args, varargs, varkw, locals)``. *args* is a list of the
389 argument names (it may contain nested lists). *varargs* and *varkw* are the
390 names of the ``*`` and ``**`` arguments or ``None``. *locals* is the locals
391 dictionary of the given frame.
392
393
394.. function:: formatargspec(args[, varargs, varkw, defaults, formatarg, formatvarargs, formatvarkw, formatvalue, join])
395
396 Format a pretty argument spec from the four values returned by
397 :func:`getargspec`. The format\* arguments are the corresponding optional
398 formatting functions that are called to turn names and values into strings.
399
400
401.. function:: formatargvalues(args[, varargs, varkw, locals, formatarg, formatvarargs, formatvarkw, formatvalue, join])
402
403 Format a pretty argument spec from the four values returned by
404 :func:`getargvalues`. The format\* arguments are the corresponding optional
405 formatting functions that are called to turn names and values into strings.
406
407
408.. function:: getmro(cls)
409
410 Return a tuple of class cls's base classes, including cls, in method resolution
411 order. No class appears more than once in this tuple. Note that the method
412 resolution order depends on cls's type. Unless a very peculiar user-defined
413 metatype is in use, cls will be the first element of the tuple.
414
415
416.. _inspect-stack:
417
418The interpreter stack
419---------------------
420
421When the following functions return "frame records," each record is a tuple of
422six items: the frame object, the filename, the line number of the current line,
423the function name, a list of lines of context from the source code, and the
424index of the current line within that list.
425
426.. warning::
427
428 Keeping references to frame objects, as found in the first element of the frame
429 records these functions return, can cause your program to create reference
430 cycles. Once a reference cycle has been created, the lifespan of all objects
431 which can be accessed from the objects which form the cycle can become much
432 longer even if Python's optional cycle detector is enabled. If such cycles must
433 be created, it is important to ensure they are explicitly broken to avoid the
434 delayed destruction of objects and increased memory consumption which occurs.
435
436 Though the cycle detector will catch these, destruction of the frames (and local
437 variables) can be made deterministic by removing the cycle in a
438 :keyword:`finally` clause. This is also important if the cycle detector was
439 disabled when Python was compiled or using :func:`gc.disable`. For example::
440
441 def handle_stackframe_without_leak():
442 frame = inspect.currentframe()
443 try:
444 # do something with the frame
445 finally:
446 del frame
447
448The optional *context* argument supported by most of these functions specifies
449the number of lines of context to return, which are centered around the current
450line.
451
452
453.. function:: getframeinfo(frame[, context])
454
455 Get information about a frame or traceback object. A 5-tuple is returned, the
456 last five elements of the frame's frame record.
457
458
459.. function:: getouterframes(frame[, context])
460
461 Get a list of frame records for a frame and all outer frames. These frames
462 represent the calls that lead to the creation of *frame*. The first entry in the
463 returned list represents *frame*; the last entry represents the outermost call
464 on *frame*'s stack.
465
466
467.. function:: getinnerframes(traceback[, context])
468
469 Get a list of frame records for a traceback's frame and all inner frames. These
470 frames represent calls made as a consequence of *frame*. The first entry in the
471 list represents *traceback*; the last entry represents where the exception was
472 raised.
473
474
475.. function:: currentframe()
476
477 Return the frame object for the caller's stack frame.
478
479
480.. function:: stack([context])
481
482 Return a list of frame records for the caller's stack. The first entry in the
483 returned list represents the caller; the last entry represents the outermost
484 call on the stack.
485
486
487.. function:: trace([context])
488
489 Return a list of frame records for the stack between the current frame and the
490 frame in which an exception currently being handled was raised in. The first
491 entry in the list represents the caller; the last entry represents where the
492 exception was raised.
493