394 lines
17 KiB
TeX
394 lines
17 KiB
TeX
\section{\module{inspect} ---
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Inspect live objects}
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\declaremodule{standard}{inspect}
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\modulesynopsis{Extract information and source code from live objects.}
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\moduleauthor{Ka-Ping Yee}{ping@lfw.org}
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\sectionauthor{Ka-Ping Yee}{ping@lfw.org}
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\versionadded{2.1}
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The \module{inspect} module provides several useful functions
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to help get information about live objects such as modules,
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classes, methods, functions, tracebacks, frame objects, and
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code objects. For example, it can help you examine the
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contents of a class, retrieve the source code of a method,
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extract and format the argument list for a function, or
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get all the information you need to display a detailed traceback.
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There are four main kinds of services provided by this module:
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type checking, getting source code, inspecting classes
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and functions, and examining the interpreter stack.
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\subsection{Types and members
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\label{inspect-types}}
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The \function{getmembers()} function retrieves the members
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of an object such as a class or module.
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The eleven functions whose names begin with ``is'' are mainly
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provided as convenient choices for the second argument to
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\function{getmembers()}. They also help you determine when
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you can expect to find the following special attributes:
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\begin{tableiv}{c|l|l|c}{}{Type}{Attribute}{Description}{Notes}
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\lineiv{module}{__doc__}{documentation string}{}
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\lineiv{}{__file__}{filename (missing for built-in modules)}{}
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\hline
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\lineiv{class}{__doc__}{documentation string}{}
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\lineiv{}{__module__}{name of module in which this class was defined}{}
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\hline
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\lineiv{method}{__doc__}{documentation string}{}
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\lineiv{}{__name__}{name with which this method was defined}{}
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\lineiv{}{im_class}{class object that asked for this method}{(1)}
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\lineiv{}{im_func}{function object containing implementation of method}{}
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\lineiv{}{im_self}{instance to which this method is bound, or \code{None}}{}
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\hline
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\lineiv{function}{__doc__}{documentation string}{}
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\lineiv{}{__name__}{name with which this function was defined}{}
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\lineiv{}{func_code}{code object containing compiled function bytecode}{}
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\lineiv{}{func_defaults}{tuple of any default values for arguments}{}
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\lineiv{}{func_doc}{(same as __doc__)}{}
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\lineiv{}{func_globals}{global namespace in which this function was defined}{}
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\lineiv{}{func_name}{(same as __name__)}{}
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\hline
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\lineiv{traceback}{tb_frame}{frame object at this level}{}
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\lineiv{}{tb_lasti}{index of last attempted instruction in bytecode}{}
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\lineiv{}{tb_lineno}{current line number in Python source code}{}
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\lineiv{}{tb_next}{next inner traceback object (called by this level)}{}
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\hline
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\lineiv{frame}{f_back}{next outer frame object (this frame's caller)}{}
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\lineiv{}{f_builtins}{built-in namespace seen by this frame}{}
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\lineiv{}{f_code}{code object being executed in this frame}{}
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\lineiv{}{f_exc_traceback}{traceback if raised in this frame, or \code{None}}{}
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\lineiv{}{f_exc_type}{exception type if raised in this frame, or \code{None}}{}
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\lineiv{}{f_exc_value}{exception value if raised in this frame, or \code{None}}{}
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\lineiv{}{f_globals}{global namespace seen by this frame}{}
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\lineiv{}{f_lasti}{index of last attempted instruction in bytecode}{}
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\lineiv{}{f_lineno}{current line number in Python source code}{}
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\lineiv{}{f_locals}{local namespace seen by this frame}{}
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\lineiv{}{f_restricted}{0 or 1 if frame is in restricted execution mode}{}
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\lineiv{}{f_trace}{tracing function for this frame, or \code{None}}{}
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\hline
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\lineiv{code}{co_argcount}{number of arguments (not including * or ** args)}{}
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\lineiv{}{co_code}{string of raw compiled bytecode}{}
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\lineiv{}{co_consts}{tuple of constants used in the bytecode}{}
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\lineiv{}{co_filename}{name of file in which this code object was created}{}
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\lineiv{}{co_firstlineno}{number of first line in Python source code}{}
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\lineiv{}{co_flags}{bitmap: 1=optimized \code{|} 2=newlocals \code{|} 4=*arg \code{|} 8=**arg}{}
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\lineiv{}{co_lnotab}{encoded mapping of line numbers to bytecode indices}{}
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\lineiv{}{co_name}{name with which this code object was defined}{}
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\lineiv{}{co_names}{tuple of names of local variables}{}
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\lineiv{}{co_nlocals}{number of local variables}{}
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\lineiv{}{co_stacksize}{virtual machine stack space required}{}
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\lineiv{}{co_varnames}{tuple of names of arguments and local variables}{}
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\hline
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\lineiv{builtin}{__doc__}{documentation string}{}
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\lineiv{}{__name__}{original name of this function or method}{}
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\lineiv{}{__self__}{instance to which a method is bound, or \code{None}}{}
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\end{tableiv}
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\noindent
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Note:
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\begin{description}
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\item[(1)]
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\versionchanged[\member{im_class} used to refer to the class that
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defined the method]{2.2}
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\end{description}
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\begin{funcdesc}{getmembers}{object\optional{, predicate}}
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Return all the members of an object in a list of (name, value) pairs
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sorted by name. If the optional \var{predicate} argument is supplied,
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only members for which the predicate returns a true value are included.
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\end{funcdesc}
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\begin{funcdesc}{getmoduleinfo}{path}
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Return a tuple of values that describe how Python will interpret the
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file identified by \var{path} if it is a module, or \code{None} if
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it would not be identified as a module. The return tuple is
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\code{(\var{name}, \var{suffix}, \var{mode}, \var{mtype})}, where
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\var{name} is the name of the module without the name of any
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enclosing package, \var{suffix} is the trailing part of the file
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name (which may not be a dot-delimited extension), \var{mode} is the
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\function{open()} mode that would be used (\code{'r'} or
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\code{'rb'}), and \var{mtype} is an integer giving the type of the
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module. \var{mtype} will have a value which can be compared to the
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constants defined in the \refmodule{imp} module; see the
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documentation for that module for more information on module types.
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\end{funcdesc}
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\begin{funcdesc}{getmodulename}{path}
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Return the name of the module named by the file \var{path}, without
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including the names of enclosing packages. This uses the same
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algorithm as the interpreter uses when searching for modules. If
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the name cannot be matched according to the interpreter's rules,
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\code{None} is returned.
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\end{funcdesc}
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\begin{funcdesc}{ismodule}{object}
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Return true if the object is a module.
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\end{funcdesc}
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\begin{funcdesc}{isclass}{object}
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Return true if the object is a class.
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\end{funcdesc}
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\begin{funcdesc}{ismethod}{object}
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Return true if the object is a method.
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\end{funcdesc}
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\begin{funcdesc}{isfunction}{object}
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Return true if the object is a Python function or unnamed (lambda) function.
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\end{funcdesc}
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\begin{funcdesc}{istraceback}{object}
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Return true if the object is a traceback.
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\end{funcdesc}
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\begin{funcdesc}{isframe}{object}
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Return true if the object is a frame.
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\end{funcdesc}
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\begin{funcdesc}{iscode}{object}
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Return true if the object is a code.
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\end{funcdesc}
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\begin{funcdesc}{isbuiltin}{object}
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Return true if the object is a built-in function.
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\end{funcdesc}
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\begin{funcdesc}{isroutine}{object}
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Return true if the object is a user-defined or built-in function or method.
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\end{funcdesc}
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\begin{funcdesc}{ismethoddescriptor}{object}
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Return true if the object is a method descriptor, but not if ismethod() or
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isclass() or isfunction() are true.
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This is new as of Python 2.2, and, for example, is true of int.__add__.
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An object passing this test has a __get__ attribute but not a __set__
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attribute, but beyond that the set of attributes varies. __name__ is
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usually sensible, and __doc__ often is.
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Methods implemented via descriptors that also pass one of the other
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tests return false from the ismethoddescriptor() test, simply because
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the other tests promise more -- you can, e.g., count on having the
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im_func attribute (etc) when an object passes ismethod().
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\end{funcdesc}
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\begin{funcdesc}{isdatadescriptor}{object}
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Return true if the object is a data descriptor.
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Data descriptors have both a __get__ and a __set__ attribute. Examples are
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properties (defined in Python), getsets, and members. The latter two are
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defined in C and there are more specific tests available for those types,
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which is robust across Python implementations. Typically, data descriptors
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will also have __name__ and __doc__ attributes (properties, getsets, and
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members have both of these attributes), but this is not guaranteed.
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\versionadded{2.3}
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\end{funcdesc}
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\begin{funcdesc}{isgetsetdescriptor}{object}
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Return true if the object is a getset descriptor.
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getsets are attributes defined in extension modules via \code{PyGetSetDef}
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structures. For Python implementations without such types, this method will
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always return \code{False}.
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\versionadded{2.5}
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\end{funcdesc}
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\begin{funcdesc}{ismemberdescriptor}{object}
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Return true if the object is a member descriptor.
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Member descriptors are attributes defined in extension modules via
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\code{PyMemberDef} structures. For Python implementations without such
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types, this method will always return \code{False}.
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\versionadded{2.5}
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\end{funcdesc}
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\subsection{Retrieving source code
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\label{inspect-source}}
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\begin{funcdesc}{getdoc}{object}
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Get the documentation string for an object.
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All tabs are expanded to spaces. To clean up docstrings that are
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indented to line up with blocks of code, any whitespace than can be
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uniformly removed from the second line onwards is removed.
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\end{funcdesc}
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\begin{funcdesc}{getcomments}{object}
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Return in a single string any lines of comments immediately preceding
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the object's source code (for a class, function, or method), or at the
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top of the Python source file (if the object is a module).
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\end{funcdesc}
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\begin{funcdesc}{getfile}{object}
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Return the name of the (text or binary) file in which an object was
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defined. This will fail with a \exception{TypeError} if the object
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is a built-in module, class, or function.
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\end{funcdesc}
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\begin{funcdesc}{getmodule}{object}
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Try to guess which module an object was defined in.
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\end{funcdesc}
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\begin{funcdesc}{getsourcefile}{object}
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Return the name of the Python source file in which an object was
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defined. This will fail with a \exception{TypeError} if the object
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is a built-in module, class, or function.
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\end{funcdesc}
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\begin{funcdesc}{getsourcelines}{object}
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Return a list of source lines and starting line number for an object.
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The argument may be a module, class, method, function, traceback, frame,
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or code object. The source code is returned as a list of the lines
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corresponding to the object and the line number indicates where in the
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original source file the first line of code was found. An
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\exception{IOError} is raised if the source code cannot be retrieved.
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\end{funcdesc}
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\begin{funcdesc}{getsource}{object}
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Return the text of the source code for an object.
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The argument may be a module, class, method, function, traceback, frame,
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or code object. The source code is returned as a single string. An
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\exception{IOError} is raised if the source code cannot be retrieved.
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\end{funcdesc}
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\subsection{Classes and functions
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\label{inspect-classes-functions}}
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\begin{funcdesc}{getclasstree}{classes\optional{, unique}}
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Arrange the given list of classes into a hierarchy of nested lists.
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Where a nested list appears, it contains classes derived from the class
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whose entry immediately precedes the list. Each entry is a 2-tuple
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containing a class and a tuple of its base classes. If the \var{unique}
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argument is true, exactly one entry appears in the returned structure
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for each class in the given list. Otherwise, classes using multiple
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inheritance and their descendants will appear multiple times.
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\end{funcdesc}
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\begin{funcdesc}{getargspec}{func}
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Get the names and default values of a function's arguments.
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A tuple of four things is returned: \code{(\var{args},
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\var{varargs}, \var{varkw}, \var{defaults})}.
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\var{args} is a list of the argument names (it may contain nested lists).
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\var{varargs} and \var{varkw} are the names of the \code{*} and
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\code{**} arguments or \code{None}.
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\var{defaults} is a tuple of default argument values or None if there are no
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default arguments; if this tuple has \var{n} elements, they correspond to
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the last \var{n} elements listed in \var{args}.
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\end{funcdesc}
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\begin{funcdesc}{getargvalues}{frame}
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Get information about arguments passed into a particular frame.
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A tuple of four things is returned: \code{(\var{args},
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\var{varargs}, \var{varkw}, \var{locals})}.
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\var{args} is a list of the argument names (it may contain nested
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lists).
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\var{varargs} and \var{varkw} are the names of the \code{*} and
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\code{**} arguments or \code{None}.
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\var{locals} is the locals dictionary of the given frame.
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\end{funcdesc}
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\begin{funcdesc}{formatargspec}{args\optional{, varargs, varkw, defaults,
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formatarg, formatvarargs, formatvarkw, formatvalue, join}}
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Format a pretty argument spec from the four values returned by
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\function{getargspec()}. The format* arguments are the
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corresponding optional formatting functions that are called to turn
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names and values into strings.
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\end{funcdesc}
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\begin{funcdesc}{formatargvalues}{args\optional{, varargs, varkw, locals,
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formatarg, formatvarargs, formatvarkw, formatvalue, join}}
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Format a pretty argument spec from the four values returned by
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\function{getargvalues()}. The format* arguments are the
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corresponding optional formatting functions that are called to turn
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names and values into strings.
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\end{funcdesc}
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\begin{funcdesc}{getmro}{cls}
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Return a tuple of class cls's base classes, including cls, in
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method resolution order. No class appears more than once in this tuple.
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Note that the method resolution order depends on cls's type. Unless a
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very peculiar user-defined metatype is in use, cls will be the first
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element of the tuple.
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\end{funcdesc}
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\subsection{The interpreter stack
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\label{inspect-stack}}
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When the following functions return ``frame records,'' each record
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is a tuple of six items: the frame object, the filename,
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the line number of the current line, the function name, a list of
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lines of context from the source code, and the index of the current
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line within that list.
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\begin{notice}[warning]
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Keeping references to frame objects, as found in
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the first element of the frame records these functions return, can
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cause your program to create reference cycles. Once a reference cycle
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has been created, the lifespan of all objects which can be accessed
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from the objects which form the cycle can become much longer even if
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Python's optional cycle detector is enabled. If such cycles must be
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created, it is important to ensure they are explicitly broken to avoid
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the delayed destruction of objects and increased memory consumption
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which occurs.
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Though the cycle detector will catch these, destruction of the frames
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(and local variables) can be made deterministic by removing the cycle
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in a \keyword{finally} clause. This is also important if the cycle
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detector was disabled when Python was compiled or using
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\function{\refmodule{gc}.disable()}. For example:
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\begin{verbatim}
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def handle_stackframe_without_leak():
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frame = inspect.currentframe()
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try:
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# do something with the frame
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finally:
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del frame
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\end{verbatim}
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\end{notice}
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The optional \var{context} argument supported by most of these
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functions specifies the number of lines of context to return, which
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are centered around the current line.
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\begin{funcdesc}{getframeinfo}{frame\optional{, context}}
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Get information about a frame or traceback object. A 5-tuple
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is returned, the last five elements of the frame's frame record.
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\end{funcdesc}
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\begin{funcdesc}{getouterframes}{frame\optional{, context}}
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Get a list of frame records for a frame and all outer frames. These
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frames represent the calls that lead to the creation of \var{frame}.
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The first entry in the returned list represents \var{frame}; the
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last entry represents the outermost call on \var{frame}'s stack.
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\end{funcdesc}
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\begin{funcdesc}{getinnerframes}{traceback\optional{, context}}
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Get a list of frame records for a traceback's frame and all inner
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frames. These frames represent calls made as a consequence of
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\var{frame}. The first entry in the list represents
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\var{traceback}; the last entry represents where the exception was
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raised.
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\end{funcdesc}
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\begin{funcdesc}{currentframe}{}
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Return the frame object for the caller's stack frame.
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\end{funcdesc}
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\begin{funcdesc}{stack}{\optional{context}}
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Return a list of frame records for the caller's stack. The first
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entry in the returned list represents the caller; the last entry
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represents the outermost call on the stack.
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\end{funcdesc}
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\begin{funcdesc}{trace}{\optional{context}}
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Return a list of frame records for the stack between the current
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frame and the frame in which an exception currently being handled
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was raised in. The first entry in the list represents the caller;
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the last entry represents where the exception was raised.
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\end{funcdesc}
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