28.13. inspect — Inspect live objects

New in version 2.1.

Source code: Lib/inspect.py


The 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.

28.13.1. Types and members

The getmembers() function retrieves the members of an object such as a class or module. The sixteen functions whose names begin with “is” are mainly provided as convenient choices for the second argument to 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 for this method (1)
  im_func or __func__ function object containing implementation of method  
  im_self or __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__)  
generator __iter__ defined to support iteration over container  
  close raises new GeneratorExit exception inside the generator to terminate the iteration  
  gi_code code object  
  gi_frame frame object or possibly None once the generator has been exhausted  
  gi_running set to 1 when generator is executing, 0 otherwise  
  next return the next item from the container  
  send resumes the generator and “sends” a value that becomes the result of the current yield-expression  
  throw used to raise an exception inside the generator  
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 builtins 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. Changed in version 2.2: im_class used to refer to the class that defined the method.

inspect.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.

Note

getmembers() does not return metaclass attributes when the argument is a class (this behavior is inherited from the dir() function).

inspect.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, module_type), 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 open() mode that would be used ('r' or 'rb'), and module_type is an integer giving the type of the module. module_type will have a value which can be compared to the constants defined in the imp module; see the documentation for that module for more information on module types.

Changed in version 2.6: Returns a named tuple ModuleInfo(name, suffix, mode, module_type).

inspect.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.

inspect.ismodule(object)

Return true if the object is a module.

inspect.isclass(object)

Return true if the object is a class, whether built-in or created in Python code.

inspect.ismethod(object)

Return true if the object is a bound or unbound method written in Python.

inspect.isfunction(object)

Return true if the object is a Python function, which includes functions created by a lambda expression.

inspect.isgeneratorfunction(object)

Return true if the object is a Python generator function.

New in version 2.6.

inspect.isgenerator(object)

Return true if the object is a generator.

New in version 2.6.

inspect.istraceback(object)

Return true if the object is a traceback.

inspect.isframe(object)

Return true if the object is a frame.

inspect.iscode(object)

Return true if the object is a code.

inspect.isbuiltin(object)

Return true if the object is a built-in function or a bound built-in method.

inspect.isroutine(object)

Return true if the object is a user-defined or built-in function or method.

inspect.isabstract(object)

Return true if the object is an abstract base class.

New in version 2.6.

inspect.ismethoddescriptor(object)

Return true if the object is a method descriptor, but not if ismethod(), isclass(), isfunction() or isbuiltin() 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().

inspect.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.

New in version 2.3.

inspect.isgetsetdescriptor(object)

Return true if the object is a getset descriptor.

CPython implementation detail: getsets are attributes defined in extension modules via PyGetSetDef structures. For Python implementations without such types, this method will always return False.

New in version 2.5.

inspect.ismemberdescriptor(object)

Return true if the object is a member descriptor.

CPython implementation detail: Member descriptors are attributes defined in extension modules via PyMemberDef structures. For Python implementations without such types, this method will always return False.

New in version 2.5.

28.13.2. Retrieving source code

inspect.getdoc(object)

Get the documentation string for an object, cleaned up with cleandoc().

inspect.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).

inspect.getfile(object)

Return the name of the (text or binary) file in which an object was defined. This will fail with a TypeError if the object is a built-in module, class, or function.

inspect.getmodule(object)

Try to guess which module an object was defined in.

inspect.getsourcefile(object)

Return the name of the Python source file in which an object was defined. This will fail with a TypeError if the object is a built-in module, class, or function.

inspect.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 IOError is raised if the source code cannot be retrieved.

inspect.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 IOError is raised if the source code cannot be retrieved.

inspect.cleandoc(doc)

Clean up indentation from docstrings that are indented to line up with blocks of code.

All leading whitespace is removed from the first line. Any leading whitespace that can be uniformly removed from the second line onwards is removed. Empty lines at the beginning and end are subsequently removed. Also, all tabs are expanded to spaces.

New in version 2.6.

28.13.3. Classes and functions

inspect.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.

inspect.getargspec(func)

Get the names and default values of a Python function’s arguments. A tuple of four things is returned: (args, varargs, keywords, defaults). args is a list of the argument names (it may contain nested lists). varargs and keywords 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.

Changed in version 2.6: Returns a named tuple ArgSpec(args, varargs, keywords, defaults).

inspect.getargvalues(frame)

Get information about arguments passed into a particular frame. A tuple of four things is returned: (args, varargs, keywords, locals). args is a list of the argument names (it may contain nested lists). varargs and keywords are the names of the * and ** arguments or None. locals is the locals dictionary of the given frame.

Changed in version 2.6: Returns a named tuple ArgInfo(args, varargs, keywords, locals).

inspect.formatargspec(args[, varargs, varkw, defaults, formatarg, formatvarargs, formatvarkw, formatvalue, join])

Format a pretty argument spec from the four values returned by getargspec(). The format* arguments are the corresponding optional formatting functions that are called to turn names and values into strings.

inspect.formatargvalues(args[, varargs, varkw, locals, formatarg, formatvarargs, formatvarkw, formatvalue, join])

Format a pretty argument spec from the four values returned by getargvalues(). The format* arguments are the corresponding optional formatting functions that are called to turn names and values into strings.

inspect.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.getcallargs(func[, *args][, **kwds])

Bind the args and kwds to the argument names of the Python function or method func, as if it was called with them. For bound methods, bind also the first argument (typically named self) to the associated instance. A dict is returned, mapping the argument names (including the names of the * and ** arguments, if any) to their values from args and kwds. In case of invoking func incorrectly, i.e. whenever func(*args, **kwds) would raise an exception because of incompatible signature, an exception of the same type and the same or similar message is raised. For example:

>>> from inspect import getcallargs
>>> def f(a, b=1, *pos, **named):
...     pass
>>> getcallargs(f, 1, 2, 3)
{'a': 1, 'named': {}, 'b': 2, 'pos': (3,)}
>>> getcallargs(f, a=2, x=4)
{'a': 2, 'named': {'x': 4}, 'b': 1, 'pos': ()}
>>> getcallargs(f)
Traceback (most recent call last):
...
TypeError: f() takes at least 1 argument (0 given)

New in version 2.7.

28.13.4. 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.

Note

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 finally clause. This is also important if the cycle detector was disabled when Python was compiled or using 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.

inspect.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.

Changed in version 2.6: Returns a named tuple Traceback(filename, lineno, function, code_context, index).

inspect.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.

inspect.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.

inspect.currentframe()

Return the frame object for the caller’s stack frame.

CPython implementation detail: This function relies on Python stack frame support in the interpreter, which isn’t guaranteed to exist in all implementations of Python. If running in an implementation without Python stack frame support this function returns None.

inspect.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.

inspect.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.