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