13. inspect
— Inspect live objects¶
New in version 2.1.
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.
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:
Changed in version 2.2:
im_class
used to refer to the class that defined the method.
-
inspect.
getmembers
(object[, predicate])[source]¶ 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 thedir()
function).
-
inspect.
getmoduleinfo
(path)[source]¶ 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 theopen()
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 theimp
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)[source]¶ 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.
isclass
(object)[source]¶ Return true if the object is a class, whether built-in or created in Python code.
-
inspect.
ismethod
(object)[source]¶ Return true if the object is a bound or unbound method written in Python.
-
inspect.
isfunction
(object)[source]¶ Return true if the object is a Python function, which includes functions created by a lambda expression.
-
inspect.
isgeneratorfunction
(object)[source]¶ Return true if the object is a Python generator function.
New in version 2.6.
-
inspect.
isbuiltin
(object)[source]¶ Return true if the object is a built-in function or a bound built-in method.
-
inspect.
isroutine
(object)[source]¶ Return true if the object is a user-defined or built-in function or method.
-
inspect.
isabstract
(object)[source]¶ Return true if the object is an abstract base class.
New in version 2.6.
-
inspect.
ismethoddescriptor
(object)[source]¶ Return true if the object is a method descriptor, but not if
ismethod()
,isclass()
,isfunction()
orisbuiltin()
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 theim_func
attribute (etc) when an object passesismethod()
.
-
inspect.
isdatadescriptor
(object)[source]¶ 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.
13.2. Retrieving source code¶
-
inspect.
getdoc
(object)[source]¶ Get the documentation string for an object, cleaned up with
cleandoc()
.
-
inspect.
getcomments
(object)[source]¶ 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)[source]¶ 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.
getsourcefile
(object)[source]¶ 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)[source]¶ 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.
13.3. Classes and functions¶
-
inspect.
getclasstree
(classes[, unique])[source]¶ 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)[source]¶ 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 orNone
. 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)[source]¶ 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 orNone
. 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])[source]¶ 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])[source]¶ 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.
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inspect.
getmro
(cls)[source]¶ 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])[source]¶ 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. wheneverfunc(*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.
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])[source]¶ 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])[source]¶ 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])[source]¶ 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.