source: python/trunk/Doc/library/inspect.rst

Last change on this file was 391, checked in by dmik, 11 years ago

python: Merge vendor 2.7.6 to trunk.
  • Property svn:eol-style set to native
File size: 27.2 KB
RevLine 
[2]1:mod:`inspect` --- Inspect live objects
2=======================================
3
4.. module:: inspect
5 :synopsis: Extract information and source code from live objects.
6.. moduleauthor:: Ka-Ping Yee <ping@lfw.org>
7.. sectionauthor:: Ka-Ping Yee <ping@lfw.org>
8
9
10.. versionadded:: 2.1
11
[391]12**Source code:** :source:`Lib/inspect.py`
13
14--------------
15
[2]16The :mod:`inspect` module provides several useful functions to help get
17information about live objects such as modules, classes, methods, functions,
18tracebacks, frame objects, and code objects. For example, it can help you
19examine the contents of a class, retrieve the source code of a method, extract
20and format the argument list for a function, or get all the information you need
21to display a detailed traceback.
22
23There are four main kinds of services provided by this module: type checking,
24getting source code, inspecting classes and functions, and examining the
25interpreter stack.
26
27
28.. _inspect-types:
29
30Types and members
31-----------------
32
33The :func:`getmembers` function retrieves the members of an object such as a
34class or module. The sixteen functions whose names begin with "is" are mainly
35provided as convenient choices for the second argument to :func:`getmembers`.
36They also help you determine when you can expect to find the following special
37attributes:
38
39+-----------+-----------------+---------------------------+-------+
40| Type | Attribute | Description | Notes |
41+===========+=================+===========================+=======+
42| module | __doc__ | documentation string | |
43+-----------+-----------------+---------------------------+-------+
44| | __file__ | filename (missing for | |
45| | | built-in modules) | |
46+-----------+-----------------+---------------------------+-------+
47| class | __doc__ | documentation string | |
48+-----------+-----------------+---------------------------+-------+
49| | __module__ | name of module in which | |
50| | | this class was defined | |
51+-----------+-----------------+---------------------------+-------+
52| method | __doc__ | documentation string | |
53+-----------+-----------------+---------------------------+-------+
54| | __name__ | name with which this | |
55| | | method was defined | |
56+-----------+-----------------+---------------------------+-------+
57| | im_class | class object that asked | \(1) |
58| | | for this method | |
59+-----------+-----------------+---------------------------+-------+
60| | im_func or | function object | |
61| | __func__ | containing implementation | |
62| | | of method | |
63+-----------+-----------------+---------------------------+-------+
64| | im_self or | instance to which this | |
65| | __self__ | method is bound, or | |
66| | | ``None`` | |
67+-----------+-----------------+---------------------------+-------+
68| function | __doc__ | documentation string | |
69+-----------+-----------------+---------------------------+-------+
70| | __name__ | name with which this | |
71| | | function was defined | |
72+-----------+-----------------+---------------------------+-------+
73| | func_code | code object containing | |
74| | | compiled function | |
75| | | :term:`bytecode` | |
76+-----------+-----------------+---------------------------+-------+
77| | func_defaults | tuple of any default | |
78| | | values for arguments | |
79+-----------+-----------------+---------------------------+-------+
80| | func_doc | (same as __doc__) | |
81+-----------+-----------------+---------------------------+-------+
82| | func_globals | global namespace in which | |
83| | | this function was defined | |
84+-----------+-----------------+---------------------------+-------+
85| | func_name | (same as __name__) | |
86+-----------+-----------------+---------------------------+-------+
87| generator | __iter__ | defined to support | |
88| | | iteration over container | |
89+-----------+-----------------+---------------------------+-------+
90| | close | raises new GeneratorExit | |
91| | | exception inside the | |
92| | | generator to terminate | |
93| | | the iteration | |
94+-----------+-----------------+---------------------------+-------+
95| | gi_code | code object | |
96+-----------+-----------------+---------------------------+-------+
97| | gi_frame | frame object or possibly | |
98| | | None once the generator | |
99| | | has been exhausted | |
100+-----------+-----------------+---------------------------+-------+
101| | gi_running | set to 1 when generator | |
102| | | is executing, 0 otherwise | |
103+-----------+-----------------+---------------------------+-------+
104| | next | return the next item from | |
105| | | the container | |
106+-----------+-----------------+---------------------------+-------+
107| | send | resumes the generator and | |
108| | | "sends" a value that | |
109| | | becomes the result of the | |
110| | | current yield-expression | |
111+-----------+-----------------+---------------------------+-------+
112| | throw | used to raise an | |
113| | | exception inside the | |
114| | | generator | |
115+-----------+-----------------+---------------------------+-------+
116| traceback | tb_frame | frame object at this | |
117| | | level | |
118+-----------+-----------------+---------------------------+-------+
119| | tb_lasti | index of last attempted | |
120| | | instruction in bytecode | |
121+-----------+-----------------+---------------------------+-------+
122| | tb_lineno | current line number in | |
123| | | Python source code | |
124+-----------+-----------------+---------------------------+-------+
125| | tb_next | next inner traceback | |
126| | | object (called by this | |
127| | | level) | |
128+-----------+-----------------+---------------------------+-------+
129| frame | f_back | next outer frame object | |
130| | | (this frame's caller) | |
131+-----------+-----------------+---------------------------+-------+
132| | f_builtins | builtins namespace seen | |
133| | | by this frame | |
134+-----------+-----------------+---------------------------+-------+
135| | f_code | code object being | |
136| | | executed in this frame | |
137+-----------+-----------------+---------------------------+-------+
138| | f_exc_traceback | traceback if raised in | |
139| | | this frame, or ``None`` | |
140+-----------+-----------------+---------------------------+-------+
141| | f_exc_type | exception type if raised | |
142| | | in this frame, or | |
143| | | ``None`` | |
144+-----------+-----------------+---------------------------+-------+
145| | f_exc_value | exception value if raised | |
146| | | in this frame, or | |
147| | | ``None`` | |
148+-----------+-----------------+---------------------------+-------+
149| | f_globals | global namespace seen by | |
150| | | this frame | |
151+-----------+-----------------+---------------------------+-------+
152| | f_lasti | index of last attempted | |
153| | | instruction in bytecode | |
154+-----------+-----------------+---------------------------+-------+
155| | f_lineno | current line number in | |
156| | | Python source code | |
157+-----------+-----------------+---------------------------+-------+
158| | f_locals | local namespace seen by | |
159| | | this frame | |
160+-----------+-----------------+---------------------------+-------+
161| | f_restricted | 0 or 1 if frame is in | |
162| | | restricted execution mode | |
163+-----------+-----------------+---------------------------+-------+
164| | f_trace | tracing function for this | |
165| | | frame, or ``None`` | |
166+-----------+-----------------+---------------------------+-------+
167| code | co_argcount | number of arguments (not | |
168| | | including \* or \*\* | |
169| | | args) | |
170+-----------+-----------------+---------------------------+-------+
171| | co_code | string of raw compiled | |
172| | | bytecode | |
173+-----------+-----------------+---------------------------+-------+
174| | co_consts | tuple of constants used | |
175| | | in the bytecode | |
176+-----------+-----------------+---------------------------+-------+
177| | co_filename | name of file in which | |
178| | | this code object was | |
179| | | created | |
180+-----------+-----------------+---------------------------+-------+
181| | co_firstlineno | number of first line in | |
182| | | Python source code | |
183+-----------+-----------------+---------------------------+-------+
184| | co_flags | bitmap: 1=optimized ``|`` | |
185| | | 2=newlocals ``|`` 4=\*arg | |
186| | | ``|`` 8=\*\*arg | |
187+-----------+-----------------+---------------------------+-------+
188| | co_lnotab | encoded mapping of line | |
189| | | numbers to bytecode | |
190| | | indices | |
191+-----------+-----------------+---------------------------+-------+
192| | co_name | name with which this code | |
193| | | object was defined | |
194+-----------+-----------------+---------------------------+-------+
195| | co_names | tuple of names of local | |
196| | | variables | |
197+-----------+-----------------+---------------------------+-------+
198| | co_nlocals | number of local variables | |
199+-----------+-----------------+---------------------------+-------+
200| | co_stacksize | virtual machine stack | |
201| | | space required | |
202+-----------+-----------------+---------------------------+-------+
203| | co_varnames | tuple of names of | |
204| | | arguments and local | |
205| | | variables | |
206+-----------+-----------------+---------------------------+-------+
207| builtin | __doc__ | documentation string | |
208+-----------+-----------------+---------------------------+-------+
209| | __name__ | original name of this | |
210| | | function or method | |
211+-----------+-----------------+---------------------------+-------+
212| | __self__ | instance to which a | |
213| | | method is bound, or | |
214| | | ``None`` | |
215+-----------+-----------------+---------------------------+-------+
216
217Note:
218
219(1)
220 .. versionchanged:: 2.2
221 :attr:`im_class` used to refer to the class that defined the method.
222
223
224.. function:: getmembers(object[, predicate])
225
226 Return all the members of an object in a list of (name, value) pairs sorted by
227 name. If the optional *predicate* argument is supplied, only members for which
228 the predicate returns a true value are included.
229
230 .. note::
231
232 :func:`getmembers` does not return metaclass attributes when the argument
233 is a class (this behavior is inherited from the :func:`dir` function).
234
235
236.. function:: getmoduleinfo(path)
237
238 Return a tuple of values that describe how Python will interpret the file
239 identified by *path* if it is a module, or ``None`` if it would not be
[391]240 identified as a module. The return tuple is ``(name, suffix, mode,
241 module_type)``, where *name* is the name of the module without the name of
242 any enclosing package, *suffix* is the trailing part of the file name (which
243 may not be a dot-delimited extension), *mode* is the :func:`open` mode that
244 would be used (``'r'`` or ``'rb'``), and *module_type* is an integer giving
245 the type of the module. *module_type* will have a value which can be
246 compared to the constants defined in the :mod:`imp` module; see the
247 documentation for that module for more information on module types.
[2]248
249 .. versionchanged:: 2.6
250 Returns a :term:`named tuple` ``ModuleInfo(name, suffix, mode,
251 module_type)``.
252
253
254.. function:: getmodulename(path)
255
256 Return the name of the module named by the file *path*, without including the
257 names of enclosing packages. This uses the same algorithm as the interpreter
258 uses when searching for modules. If the name cannot be matched according to the
259 interpreter's rules, ``None`` is returned.
260
261
262.. function:: ismodule(object)
263
264 Return true if the object is a module.
265
266
267.. function:: isclass(object)
268
[391]269 Return true if the object is a class, whether built-in or created in Python
270 code.
[2]271
272
273.. function:: ismethod(object)
274
[391]275 Return true if the object is a bound method written in Python.
[2]276
277
278.. function:: isfunction(object)
279
[391]280 Return true if the object is a Python function, which includes functions
281 created by a :term:`lambda` expression.
[2]282
[391]283
[2]284.. function:: isgeneratorfunction(object)
285
286 Return true if the object is a Python generator function.
287
288 .. versionadded:: 2.6
289
[391]290
[2]291.. function:: isgenerator(object)
292
293 Return true if the object is a generator.
294
295 .. versionadded:: 2.6
296
[391]297
[2]298.. function:: istraceback(object)
299
300 Return true if the object is a traceback.
301
302
303.. function:: isframe(object)
304
305 Return true if the object is a frame.
306
307
308.. function:: iscode(object)
309
310 Return true if the object is a code.
311
312
313.. function:: isbuiltin(object)
314
[391]315 Return true if the object is a built-in function or a bound built-in method.
[2]316
317
318.. function:: isroutine(object)
319
320 Return true if the object is a user-defined or built-in function or method.
321
[391]322
[2]323.. function:: isabstract(object)
324
325 Return true if the object is an abstract base class.
326
327 .. versionadded:: 2.6
328
329
330.. function:: ismethoddescriptor(object)
331
[391]332 Return true if the object is a method descriptor, but not if
333 :func:`ismethod`, :func:`isclass`, :func:`isfunction` or :func:`isbuiltin`
334 are true.
[2]335
336 This is new as of Python 2.2, and, for example, is true of
337 ``int.__add__``. An object passing this test has a :attr:`__get__` attribute
338 but not a :attr:`__set__` attribute, but beyond that the set of attributes
339 varies. :attr:`__name__` is usually sensible, and :attr:`__doc__` often is.
340
341 Methods implemented via descriptors that also pass one of the other tests
342 return false from the :func:`ismethoddescriptor` test, simply because the
343 other tests promise more -- you can, e.g., count on having the
344 :attr:`im_func` attribute (etc) when an object passes :func:`ismethod`.
345
346
347.. function:: isdatadescriptor(object)
348
349 Return true if the object is a data descriptor.
350
351 Data descriptors have both a :attr:`__get__` and a :attr:`__set__` attribute.
352 Examples are properties (defined in Python), getsets, and members. The
353 latter two are defined in C and there are more specific tests available for
354 those types, which is robust across Python implementations. Typically, data
355 descriptors will also have :attr:`__name__` and :attr:`__doc__` attributes
356 (properties, getsets, and members have both of these attributes), but this is
357 not guaranteed.
358
359 .. versionadded:: 2.3
360
361
362.. function:: isgetsetdescriptor(object)
363
364 Return true if the object is a getset descriptor.
365
366 .. impl-detail::
367
368 getsets are attributes defined in extension modules via
[391]369 :c:type:`PyGetSetDef` structures. For Python implementations without such
[2]370 types, this method will always return ``False``.
371
372 .. versionadded:: 2.5
373
374
375.. function:: ismemberdescriptor(object)
376
377 Return true if the object is a member descriptor.
378
379 .. impl-detail::
380
381 Member descriptors are attributes defined in extension modules via
[391]382 :c:type:`PyMemberDef` structures. For Python implementations without such
[2]383 types, this method will always return ``False``.
384
385 .. versionadded:: 2.5
386
387
388.. _inspect-source:
389
390Retrieving source code
391----------------------
392
393.. function:: getdoc(object)
394
395 Get the documentation string for an object, cleaned up with :func:`cleandoc`.
396
397
398.. function:: getcomments(object)
399
400 Return in a single string any lines of comments immediately preceding the
401 object's source code (for a class, function, or method), or at the top of the
402 Python source file (if the object is a module).
403
404
405.. function:: getfile(object)
406
407 Return the name of the (text or binary) file in which an object was defined.
408 This will fail with a :exc:`TypeError` if the object is a built-in module,
409 class, or function.
410
411
412.. function:: getmodule(object)
413
414 Try to guess which module an object was defined in.
415
416
417.. function:: getsourcefile(object)
418
419 Return the name of the Python source file in which an object was defined. This
420 will fail with a :exc:`TypeError` if the object is a built-in module, class, or
421 function.
422
423
424.. function:: getsourcelines(object)
425
426 Return a list of source lines and starting line number for an object. The
427 argument may be a module, class, method, function, traceback, frame, or code
428 object. The source code is returned as a list of the lines corresponding to the
429 object and the line number indicates where in the original source file the first
430 line of code was found. An :exc:`IOError` is raised if the source code cannot
431 be retrieved.
432
433
434.. function:: getsource(object)
435
436 Return the text of the source code for an object. The argument may be a module,
437 class, method, function, traceback, frame, or code object. The source code is
438 returned as a single string. An :exc:`IOError` is raised if the source code
439 cannot be retrieved.
440
441
442.. function:: cleandoc(doc)
443
444 Clean up indentation from docstrings that are indented to line up with blocks
445 of code. Any whitespace that can be uniformly removed from the second line
446 onwards is removed. Also, all tabs are expanded to spaces.
447
448 .. versionadded:: 2.6
449
450
451.. _inspect-classes-functions:
452
453Classes and functions
454---------------------
455
456
457.. function:: getclasstree(classes[, unique])
458
459 Arrange the given list of classes into a hierarchy of nested lists. Where a
460 nested list appears, it contains classes derived from the class whose entry
461 immediately precedes the list. Each entry is a 2-tuple containing a class and a
462 tuple of its base classes. If the *unique* argument is true, exactly one entry
463 appears in the returned structure for each class in the given list. Otherwise,
464 classes using multiple inheritance and their descendants will appear multiple
465 times.
466
467
468.. function:: getargspec(func)
469
[391]470 Get the names and default values of a Python function's arguments. A tuple of
471 four things is returned: ``(args, varargs, keywords, defaults)``. *args* is a
472 list of the argument names (it may contain nested lists). *varargs* and
473 *keywords* are the names of the ``*`` and ``**`` arguments or
474 ``None``. *defaults* is a tuple of default argument values or None if there
475 are no default arguments; if this tuple has *n* elements, they correspond to
476 the last *n* elements listed in *args*.
[2]477
478 .. versionchanged:: 2.6
479 Returns a :term:`named tuple` ``ArgSpec(args, varargs, keywords,
480 defaults)``.
481
482
483.. function:: getargvalues(frame)
484
[391]485 Get information about arguments passed into a particular frame. A tuple of
486 four things is returned: ``(args, varargs, keywords, locals)``. *args* is a
487 list of the argument names (it may contain nested lists). *varargs* and
488 *keywords* are the names of the ``*`` and ``**`` arguments or ``None``.
489 *locals* is the locals dictionary of the given frame.
[2]490
491 .. versionchanged:: 2.6
492 Returns a :term:`named tuple` ``ArgInfo(args, varargs, keywords,
493 locals)``.
494
495
496.. function:: formatargspec(args[, varargs, varkw, defaults, formatarg, formatvarargs, formatvarkw, formatvalue, join])
497
498 Format a pretty argument spec from the four values returned by
499 :func:`getargspec`. The format\* arguments are the corresponding optional
500 formatting functions that are called to turn names and values into strings.
501
502
503.. function:: formatargvalues(args[, varargs, varkw, locals, formatarg, formatvarargs, formatvarkw, formatvalue, join])
504
505 Format a pretty argument spec from the four values returned by
506 :func:`getargvalues`. The format\* arguments are the corresponding optional
507 formatting functions that are called to turn names and values into strings.
508
509
510.. function:: getmro(cls)
511
512 Return a tuple of class cls's base classes, including cls, in method resolution
513 order. No class appears more than once in this tuple. Note that the method
514 resolution order depends on cls's type. Unless a very peculiar user-defined
515 metatype is in use, cls will be the first element of the tuple.
516
517
[391]518.. function:: getcallargs(func[, *args][, **kwds])
519
520 Bind the *args* and *kwds* to the argument names of the Python function or
521 method *func*, as if it was called with them. For bound methods, bind also the
522 first argument (typically named ``self``) to the associated instance. A dict
523 is returned, mapping the argument names (including the names of the ``*`` and
524 ``**`` arguments, if any) to their values from *args* and *kwds*. In case of
525 invoking *func* incorrectly, i.e. whenever ``func(*args, **kwds)`` would raise
526 an exception because of incompatible signature, an exception of the same type
527 and the same or similar message is raised. For example::
528
529 >>> from inspect import getcallargs
530 >>> def f(a, b=1, *pos, **named):
531 ... pass
532 >>> getcallargs(f, 1, 2, 3)
533 {'a': 1, 'named': {}, 'b': 2, 'pos': (3,)}
534 >>> getcallargs(f, a=2, x=4)
535 {'a': 2, 'named': {'x': 4}, 'b': 1, 'pos': ()}
536 >>> getcallargs(f)
537 Traceback (most recent call last):
538 ...
539 TypeError: f() takes at least 1 argument (0 given)
540
541 .. versionadded:: 2.7
542
543
[2]544.. _inspect-stack:
545
546The interpreter stack
547---------------------
548
549When the following functions return "frame records," each record is a tuple of
550six items: the frame object, the filename, the line number of the current line,
551the function name, a list of lines of context from the source code, and the
552index of the current line within that list.
553
554.. note::
555
556 Keeping references to frame objects, as found in the first element of the frame
557 records these functions return, can cause your program to create reference
558 cycles. Once a reference cycle has been created, the lifespan of all objects
559 which can be accessed from the objects which form the cycle can become much
560 longer even if Python's optional cycle detector is enabled. If such cycles must
561 be created, it is important to ensure they are explicitly broken to avoid the
562 delayed destruction of objects and increased memory consumption which occurs.
563
564 Though the cycle detector will catch these, destruction of the frames (and local
565 variables) can be made deterministic by removing the cycle in a
566 :keyword:`finally` clause. This is also important if the cycle detector was
567 disabled when Python was compiled or using :func:`gc.disable`. For example::
568
569 def handle_stackframe_without_leak():
570 frame = inspect.currentframe()
571 try:
572 # do something with the frame
573 finally:
574 del frame
575
576The optional *context* argument supported by most of these functions specifies
577the number of lines of context to return, which are centered around the current
578line.
579
580
581.. function:: getframeinfo(frame[, context])
582
583 Get information about a frame or traceback object. A 5-tuple is returned, the
584 last five elements of the frame's frame record.
585
586 .. versionchanged:: 2.6
587 Returns a :term:`named tuple` ``Traceback(filename, lineno, function,
588 code_context, index)``.
589
590
591.. function:: getouterframes(frame[, context])
592
593 Get a list of frame records for a frame and all outer frames. These frames
594 represent the calls that lead to the creation of *frame*. The first entry in the
595 returned list represents *frame*; the last entry represents the outermost call
596 on *frame*'s stack.
597
598
599.. function:: getinnerframes(traceback[, context])
600
601 Get a list of frame records for a traceback's frame and all inner frames. These
602 frames represent calls made as a consequence of *frame*. The first entry in the
603 list represents *traceback*; the last entry represents where the exception was
604 raised.
605
606
607.. function:: currentframe()
608
609 Return the frame object for the caller's stack frame.
610
611 .. impl-detail::
612
613 This function relies on Python stack frame support in the interpreter,
614 which isn't guaranteed to exist in all implementations of Python. If
615 running in an implementation without Python stack frame support this
616 function returns ``None``.
617
618
619.. function:: stack([context])
620
621 Return a list of frame records for the caller's stack. The first entry in the
622 returned list represents the caller; the last entry represents the outermost
623 call on the stack.
624
625
626.. function:: trace([context])
627
628 Return a list of frame records for the stack between the current frame and the
629 frame in which an exception currently being handled was raised in. The first
630 entry in the list represents the caller; the last entry represents where the
631 exception was raised.
632
Note: See TracBrowser for help on using the repository browser.