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authorcinap_lenrek <cinap_lenrek@localhost>2011-05-03 11:25:13 +0000
committercinap_lenrek <cinap_lenrek@localhost>2011-05-03 11:25:13 +0000
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+\section{\module{inspect} ---
+ Inspect live objects}
+
+\declaremodule{standard}{inspect}
+\modulesynopsis{Extract information and source code from live objects.}
+\moduleauthor{Ka-Ping Yee}{ping@lfw.org}
+\sectionauthor{Ka-Ping Yee}{ping@lfw.org}
+
+\versionadded{2.1}
+
+The \module{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.
+
+\subsection{Types and members
+ \label{inspect-types}}
+
+The \function{getmembers()} function retrieves the members
+of an object such as a class or module.
+The eleven functions whose names begin with ``is'' are mainly
+provided as convenient choices for the second argument to
+\function{getmembers()}. They also help you determine when
+you can expect to find the following special attributes:
+
+\begin{tableiv}{c|l|l|c}{}{Type}{Attribute}{Description}{Notes}
+ \lineiv{module}{__doc__}{documentation string}{}
+ \lineiv{}{__file__}{filename (missing for built-in modules)}{}
+ \hline
+ \lineiv{class}{__doc__}{documentation string}{}
+ \lineiv{}{__module__}{name of module in which this class was defined}{}
+ \hline
+ \lineiv{method}{__doc__}{documentation string}{}
+ \lineiv{}{__name__}{name with which this method was defined}{}
+ \lineiv{}{im_class}{class object that asked for this method}{(1)}
+ \lineiv{}{im_func}{function object containing implementation of method}{}
+ \lineiv{}{im_self}{instance to which this method is bound, or \code{None}}{}
+ \hline
+ \lineiv{function}{__doc__}{documentation string}{}
+ \lineiv{}{__name__}{name with which this function was defined}{}
+ \lineiv{}{func_code}{code object containing compiled function bytecode}{}
+ \lineiv{}{func_defaults}{tuple of any default values for arguments}{}
+ \lineiv{}{func_doc}{(same as __doc__)}{}
+ \lineiv{}{func_globals}{global namespace in which this function was defined}{}
+ \lineiv{}{func_name}{(same as __name__)}{}
+ \hline
+ \lineiv{traceback}{tb_frame}{frame object at this level}{}
+ \lineiv{}{tb_lasti}{index of last attempted instruction in bytecode}{}
+ \lineiv{}{tb_lineno}{current line number in Python source code}{}
+ \lineiv{}{tb_next}{next inner traceback object (called by this level)}{}
+ \hline
+ \lineiv{frame}{f_back}{next outer frame object (this frame's caller)}{}
+ \lineiv{}{f_builtins}{built-in namespace seen by this frame}{}
+ \lineiv{}{f_code}{code object being executed in this frame}{}
+ \lineiv{}{f_exc_traceback}{traceback if raised in this frame, or \code{None}}{}
+ \lineiv{}{f_exc_type}{exception type if raised in this frame, or \code{None}}{}
+ \lineiv{}{f_exc_value}{exception value if raised in this frame, or \code{None}}{}
+ \lineiv{}{f_globals}{global namespace seen by this frame}{}
+ \lineiv{}{f_lasti}{index of last attempted instruction in bytecode}{}
+ \lineiv{}{f_lineno}{current line number in Python source code}{}
+ \lineiv{}{f_locals}{local namespace seen by this frame}{}
+ \lineiv{}{f_restricted}{0 or 1 if frame is in restricted execution mode}{}
+ \lineiv{}{f_trace}{tracing function for this frame, or \code{None}}{}
+ \hline
+ \lineiv{code}{co_argcount}{number of arguments (not including * or ** args)}{}
+ \lineiv{}{co_code}{string of raw compiled bytecode}{}
+ \lineiv{}{co_consts}{tuple of constants used in the bytecode}{}
+ \lineiv{}{co_filename}{name of file in which this code object was created}{}
+ \lineiv{}{co_firstlineno}{number of first line in Python source code}{}
+ \lineiv{}{co_flags}{bitmap: 1=optimized \code{|} 2=newlocals \code{|} 4=*arg \code{|} 8=**arg}{}
+ \lineiv{}{co_lnotab}{encoded mapping of line numbers to bytecode indices}{}
+ \lineiv{}{co_name}{name with which this code object was defined}{}
+ \lineiv{}{co_names}{tuple of names of local variables}{}
+ \lineiv{}{co_nlocals}{number of local variables}{}
+ \lineiv{}{co_stacksize}{virtual machine stack space required}{}
+ \lineiv{}{co_varnames}{tuple of names of arguments and local variables}{}
+ \hline
+ \lineiv{builtin}{__doc__}{documentation string}{}
+ \lineiv{}{__name__}{original name of this function or method}{}
+ \lineiv{}{__self__}{instance to which a method is bound, or \code{None}}{}
+\end{tableiv}
+
+\noindent
+Note:
+\begin{description}
+\item[(1)]
+\versionchanged[\member{im_class} used to refer to the class that
+ defined the method]{2.2}
+\end{description}
+
+
+\begin{funcdesc}{getmembers}{object\optional{, predicate}}
+ Return all the members of an object in a list of (name, value) pairs
+ sorted by name. If the optional \var{predicate} argument is supplied,
+ only members for which the predicate returns a true value are included.
+\end{funcdesc}
+
+\begin{funcdesc}{getmoduleinfo}{path}
+ Return a tuple of values that describe how Python will interpret the
+ file identified by \var{path} if it is a module, or \code{None} if
+ it would not be identified as a module. The return tuple is
+ \code{(\var{name}, \var{suffix}, \var{mode}, \var{mtype})}, where
+ \var{name} is the name of the module without the name of any
+ enclosing package, \var{suffix} is the trailing part of the file
+ name (which may not be a dot-delimited extension), \var{mode} is the
+ \function{open()} mode that would be used (\code{'r'} or
+ \code{'rb'}), and \var{mtype} is an integer giving the type of the
+ module. \var{mtype} will have a value which can be compared to the
+ constants defined in the \refmodule{imp} module; see the
+ documentation for that module for more information on module types.
+\end{funcdesc}
+
+\begin{funcdesc}{getmodulename}{path}
+ Return the name of the module named by the file \var{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,
+ \code{None} is returned.
+\end{funcdesc}
+
+\begin{funcdesc}{ismodule}{object}
+ Return true if the object is a module.
+\end{funcdesc}
+
+\begin{funcdesc}{isclass}{object}
+ Return true if the object is a class.
+\end{funcdesc}
+
+\begin{funcdesc}{ismethod}{object}
+ Return true if the object is a method.
+\end{funcdesc}
+
+\begin{funcdesc}{isfunction}{object}
+ Return true if the object is a Python function or unnamed (lambda) function.
+\end{funcdesc}
+
+\begin{funcdesc}{istraceback}{object}
+ Return true if the object is a traceback.
+\end{funcdesc}
+
+\begin{funcdesc}{isframe}{object}
+ Return true if the object is a frame.
+\end{funcdesc}
+
+\begin{funcdesc}{iscode}{object}
+ Return true if the object is a code.
+\end{funcdesc}
+
+\begin{funcdesc}{isbuiltin}{object}
+ Return true if the object is a built-in function.
+\end{funcdesc}
+
+\begin{funcdesc}{isroutine}{object}
+ Return true if the object is a user-defined or built-in function or method.
+\end{funcdesc}
+
+\begin{funcdesc}{ismethoddescriptor}{object}
+ Return true if the object is a method descriptor, but not if ismethod() or
+ isclass() or isfunction() 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().
+\end{funcdesc}
+
+\begin{funcdesc}{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.
+\versionadded{2.3}
+\end{funcdesc}
+
+\begin{funcdesc}{isgetsetdescriptor}{object}
+ Return true if the object is a getset descriptor.
+
+ getsets are attributes defined in extension modules via \code{PyGetSetDef}
+ structures. For Python implementations without such types, this method will
+ always return \code{False}.
+\versionadded{2.5}
+\end{funcdesc}
+
+\begin{funcdesc}{ismemberdescriptor}{object}
+ Return true if the object is a member descriptor.
+
+ Member descriptors are attributes defined in extension modules via
+ \code{PyMemberDef} structures. For Python implementations without such
+ types, this method will always return \code{False}.
+\versionadded{2.5}
+\end{funcdesc}
+
+\subsection{Retrieving source code
+ \label{inspect-source}}
+
+\begin{funcdesc}{getdoc}{object}
+ Get the documentation string for an object.
+ All tabs are expanded to spaces. To clean up docstrings that are
+ indented to line up with blocks of code, any whitespace than can be
+ uniformly removed from the second line onwards is removed.
+\end{funcdesc}
+
+\begin{funcdesc}{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).
+\end{funcdesc}
+
+\begin{funcdesc}{getfile}{object}
+ Return the name of the (text or binary) file in which an object was
+ defined. This will fail with a \exception{TypeError} if the object
+ is a built-in module, class, or function.
+\end{funcdesc}
+
+\begin{funcdesc}{getmodule}{object}
+ Try to guess which module an object was defined in.
+\end{funcdesc}
+
+\begin{funcdesc}{getsourcefile}{object}
+ Return the name of the Python source file in which an object was
+ defined. This will fail with a \exception{TypeError} if the object
+ is a built-in module, class, or function.
+\end{funcdesc}
+
+\begin{funcdesc}{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
+ \exception{IOError} is raised if the source code cannot be retrieved.
+\end{funcdesc}
+
+\begin{funcdesc}{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
+ \exception{IOError} is raised if the source code cannot be retrieved.
+\end{funcdesc}
+
+\subsection{Classes and functions
+ \label{inspect-classes-functions}}
+
+\begin{funcdesc}{getclasstree}{classes\optional{, 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 \var{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.
+\end{funcdesc}
+
+\begin{funcdesc}{getargspec}{func}
+ Get the names and default values of a function's arguments.
+ A tuple of four things is returned: \code{(\var{args},
+ \var{varargs}, \var{varkw}, \var{defaults})}.
+ \var{args} is a list of the argument names (it may contain nested lists).
+ \var{varargs} and \var{varkw} are the names of the \code{*} and
+ \code{**} arguments or \code{None}.
+ \var{defaults} is a tuple of default argument values or None if there are no
+ default arguments; if this tuple has \var{n} elements, they correspond to
+ the last \var{n} elements listed in \var{args}.
+\end{funcdesc}
+
+\begin{funcdesc}{getargvalues}{frame}
+ Get information about arguments passed into a particular frame.
+ A tuple of four things is returned: \code{(\var{args},
+ \var{varargs}, \var{varkw}, \var{locals})}.
+ \var{args} is a list of the argument names (it may contain nested
+ lists).
+ \var{varargs} and \var{varkw} are the names of the \code{*} and
+ \code{**} arguments or \code{None}.
+ \var{locals} is the locals dictionary of the given frame.
+\end{funcdesc}
+
+\begin{funcdesc}{formatargspec}{args\optional{, varargs, varkw, defaults,
+ formatarg, formatvarargs, formatvarkw, formatvalue, join}}
+
+ Format a pretty argument spec from the four values returned by
+ \function{getargspec()}. The format* arguments are the
+ corresponding optional formatting functions that are called to turn
+ names and values into strings.
+\end{funcdesc}
+
+\begin{funcdesc}{formatargvalues}{args\optional{, varargs, varkw, locals,
+ formatarg, formatvarargs, formatvarkw, formatvalue, join}}
+ Format a pretty argument spec from the four values returned by
+ \function{getargvalues()}. The format* arguments are the
+ corresponding optional formatting functions that are called to turn
+ names and values into strings.
+\end{funcdesc}
+
+\begin{funcdesc}{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.
+\end{funcdesc}
+
+\subsection{The interpreter stack
+ \label{inspect-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.
+
+\begin{notice}[warning]
+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 \keyword{finally} clause. This is also important if the cycle
+detector was disabled when Python was compiled or using
+\function{\refmodule{gc}.disable()}. For example:
+
+\begin{verbatim}
+def handle_stackframe_without_leak():
+ frame = inspect.currentframe()
+ try:
+ # do something with the frame
+ finally:
+ del frame
+\end{verbatim}
+\end{notice}
+
+The optional \var{context} argument supported by most of these
+functions specifies the number of lines of context to return, which
+are centered around the current line.
+
+\begin{funcdesc}{getframeinfo}{frame\optional{, context}}
+ Get information about a frame or traceback object. A 5-tuple
+ is returned, the last five elements of the frame's frame record.
+\end{funcdesc}
+
+\begin{funcdesc}{getouterframes}{frame\optional{, 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 \var{frame}.
+ The first entry in the returned list represents \var{frame}; the
+ last entry represents the outermost call on \var{frame}'s stack.
+\end{funcdesc}
+
+\begin{funcdesc}{getinnerframes}{traceback\optional{, 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
+ \var{frame}. The first entry in the list represents
+ \var{traceback}; the last entry represents where the exception was
+ raised.
+\end{funcdesc}
+
+\begin{funcdesc}{currentframe}{}
+ Return the frame object for the caller's stack frame.
+\end{funcdesc}
+
+\begin{funcdesc}{stack}{\optional{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.
+\end{funcdesc}
+
+\begin{funcdesc}{trace}{\optional{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.
+\end{funcdesc}