Doc/lib/libinspect.tex

   1 \section{\module{inspect} ---
   2          Inspect live objects}
   3
   4 \declaremodule{standard}{inspect}
   5 \modulesynopsis{Extract information and source code from live objects.}
   6 \moduleauthor{Ka-Ping Yee}{ping@lfw.org}
   7 \sectionauthor{Ka-Ping Yee}{ping@lfw.org}
   8
   9 \versionadded{2.1}
  10
  11 The \module{inspect} module provides several useful functions
  12 to help get information about live objects such as modules,
  13 classes, methods, functions, tracebacks, frame objects, and
  14 code objects.  For example, it can help you examine the
  15 contents of a class, retrieve the source code of a method,
  16 extract and format the argument list for a function, or
  17 get all the information you need to display a detailed traceback.
  18
  19 There are four main kinds of services provided by this module:
  20 type checking, getting source code, inspecting classes
  21 and functions, and examining the interpreter stack.
  22
  23 \subsection{Types and members
  24             \label{inspect-types}}
  25
  26 The \function{getmembers()} function retrieves the members
  27 of an object such as a class or module.
  28 The nine functions whose names begin with ``is'' are mainly
  29 provided as convenient choices for the second argument to
  30 \function{getmembers()}.  They also help you determine when
  31 you can expect to find the following special attributes:
  32
  33 \begin{tableiii}{c|l|l}{}{Type}{Attribute}{Description}
  34   \lineiii{module}{__doc__}{documentation string}
  35   \lineiii{}{__file__}{filename (missing for built-in modules)}
  36   \hline
  37   \lineiii{class}{__doc__}{documentation string}
  38   \lineiii{}{__module__}{name of module in which this class was defined}
  39   \hline
  40   \lineiii{method}{__doc__}{documentation string}
  41   \lineiii{}{__name__}{name with which this method was defined}
  42   \lineiii{}{im_class}{class object in which this method belongs}
  43   \lineiii{}{im_func}{function object containing implementation of method}
  44   \lineiii{}{im_self}{instance to which this method is bound, or \code{None}}
  45   \hline
  46   \lineiii{function}{__doc__}{documentation string}
  47   \lineiii{}{__name__}{name with which this function was defined}
  48   \lineiii{}{func_code}{code object containing compiled function bytecode}
  49   \lineiii{}{func_defaults}{tuple of any default values for arguments}
  50   \lineiii{}{func_doc}{(same as __doc__)}
  51   \lineiii{}{func_globals}{global namespace in which this function was defined}
  52   \lineiii{}{func_name}{(same as __name__)}
  53   \hline
  54   \lineiii{traceback}{tb_frame}{frame object at this level}
  55   \lineiii{}{tb_lasti}{index of last attempted instruction in bytecode}
  56   \lineiii{}{tb_lineno}{current line number in Python source code}
  57   \lineiii{}{tb_next}{next inner traceback object (called by this level)}
  58   \hline
  59   \lineiii{frame}{f_back}{next outer frame object (this frame's caller)}
  60   \lineiii{}{f_builtins}{built-in namespace seen by this frame}
  61   \lineiii{}{f_code}{code object being executed in this frame}
  62   \lineiii{}{f_exc_traceback}{traceback if raised in this frame, or \code{None}}
  63   \lineiii{}{f_exc_type}{exception type if raised in this frame, or \code{None}}
  64   \lineiii{}{f_exc_value}{exception value if raised in this frame, or \code{None}}
  65   \lineiii{}{f_globals}{global namespace seen by this frame}
  66   \lineiii{}{f_lasti}{index of last attempted instruction in bytecode}
  67   \lineiii{}{f_lineno}{current line number in Python source code}
  68   \lineiii{}{f_locals}{local namespace seen by this frame}
  69   \lineiii{}{f_restricted}{0 or 1 if frame is in restricted execution mode}
  70   \lineiii{}{f_trace}{tracing function for this frame, or \code{None}}
  71   \hline
  72   \lineiii{code}{co_argcount}{number of arguments (not including * or ** args)}
  73   \lineiii{}{co_code}{string of raw compiled bytecode}
  74   \lineiii{}{co_consts}{tuple of constants used in the bytecode}
  75   \lineiii{}{co_filename}{name of file in which this code object was created}
  76   \lineiii{}{co_firstlineno}{number of first line in Python source code}
  77   \lineiii{}{co_flags}{bitmap: 1=optimized \code{|} 2=newlocals \code{|} 4=*arg \code{|} 8=**arg}
  78   \lineiii{}{co_lnotab}{encoded mapping of line numbers to bytecode indices}
  79   \lineiii{}{co_name}{name with which this code object was defined}
  80   \lineiii{}{co_names}{tuple of names of local variables}
  81   \lineiii{}{co_nlocals}{number of local variables}
  82   \lineiii{}{co_stacksize}{virtual machine stack space required}
  83   \lineiii{}{co_varnames}{tuple of names of arguments and local variables}
  84   \hline
  85   \lineiii{builtin}{__doc__}{documentation string}
  86   \lineiii{}{__name__}{original name of this function or method}
  87   \lineiii{}{__self__}{instance to which a method is bound, or \code{None}}
  88 \end{tableiii}
  89
  90 \begin{funcdesc}{getmembers}{object\optional{, predicate}}
  91   Return all the members of an object in a list of (name, value) pairs
  92   sorted by name.  If the optional \var{predicate} argument is supplied,
  93   only members for which the predicate returns a true value are included.
  94 \end{funcdesc}
  95
  96 \begin{funcdesc}{ismodule}{object}
  97   Return true if the object is a module.
  98 \end{funcdesc}
  99
 100 \begin{funcdesc}{isclass}{object}
 101   Return true if the object is a class.
 102 \end{funcdesc}
 103
 104 \begin{funcdesc}{ismethod}{object}
 105   Return true if the object is a method.
 106 \end{funcdesc}
 107
 108 \begin{funcdesc}{isfunction}{object}
 109   Return true if the object is a Python function or unnamed (lambda) function.
 110 \end{funcdesc}
 111
 112 \begin{funcdesc}{istraceback}{object}
 113   Return true if the object is a traceback.
 114 \end{funcdesc}
 115
 116 \begin{funcdesc}{isframe}{object}
 117   Return true if the object is a frame.
 118 \end{funcdesc}
 119
 120 \begin{funcdesc}{iscode}{object}
 121   Return true if the object is a code.
 122 \end{funcdesc}
 123
 124 \begin{funcdesc}{isbuiltin}{object}
 125   Return true if the object is a built-in function.
 126 \end{funcdesc}
 127
 128 \begin{funcdesc}{isroutine}{object}
 129   Return true if the object is a user-defined or built-in function or method.
 130 \end{funcdesc}
 131
 132 \subsection{Retrieving source code
 133             \label{inspect-source}}
 134
 135 \begin{funcdesc}{getdoc}{object}
 136   Get the documentation string for an object.
 137   All tabs are expanded to spaces.  To clean up docstrings that are
 138   indented to line up with blocks of code, any whitespace than can be
 139   uniformly removed from the second line onwards is removed.
 140 \end{funcdesc}
 141
 142 \begin{funcdesc}{getcomments}{object}
 143   Return in a single string any lines of comments immediately preceding
 144   the object's source code (for a class, function, or method), or at the
 145   top of the Python source file (if the object is a module).
 146 \end{funcdesc}
 147
 148 \begin{funcdesc}{getfile}{object}
 149   Return the name of the (text or binary) file in which an object was
 150   defined.  This will fail with a \exception{TypeError} if the object
 151   is a built-in module, class, or function.
 152 \end{funcdesc}
 153
 154 \begin{funcdesc}{getmodule}{object}
 155   Try to guess which module an object was defined in.
 156 \end{funcdesc}
 157
 158 \begin{funcdesc}{getsourcefile}{object}
 159   Return the name of the Python source file in which an object was
 160   defined.  This will fail with a \exception{TypeError} if the object
 161   is a built-in module, class, or function.
 162 \end{funcdesc}
 163
 164 \begin{funcdesc}{getsourcelines}{object}
 165   Return a list of source lines and starting line number for an object.
 166   The argument may be a module, class, method, function, traceback, frame,
 167   or code object.  The source code is returned as a list of the lines
 168   corresponding to the object and the line number indicates where in the
 169   original source file the first line of code was found.  An
 170   \exception{IOError} is raised if the source code cannot be retrieved.
 171 \end{funcdesc}
 172
 173 \begin{funcdesc}{getsource}{object}
 174   Return the text of the source code for an object.
 175   The argument may be a module, class, method, function, traceback, frame,
 176   or code object.  The source code is returned as a single string.  An
 177   \exception{IOError} is raised if the source code cannot be retrieved.
 178 \end{funcdesc}
 179
 180 \subsection{Classes and functions
 181             \label{inspect-classes-functions}}
 182
 183 \begin{funcdesc}{getclasstree}{classes\optional{, unique}}
 184   Arrange the given list of classes into a hierarchy of nested lists.
 185   Where a nested list appears, it contains classes derived from the class
 186   whose entry immediately precedes the list.  Each entry is a 2-tuple
 187   containing a class and a tuple of its base classes.  If the \var{unique}
 188   argument is true, exactly one entry appears in the returned structure
 189   for each class in the given list.  Otherwise, classes using multiple
 190   inheritance and their descendants will appear multiple times.
 191 \end{funcdesc}
 192
 193 \begin{funcdesc}{getargspec}{func}
 194   Get the names and default values of a function's arguments.
 195   A tuple of four things is returned: \code{(\var{args},
 196     \var{varargs}, \var{varkw}, \var{defaults})}.
 197   \var{args} is a list of the argument names (it may contain nested lists).
 198   \var{varargs} and \var{varkw} are the names of the \code{*} and
 199   \code{**} arguments or \code{None}.
 200   \var{defaults} is a tuple of default argument values; if this tuple
 201   has \var{n} elements, they correspond to the last \var{n} elements
 202   listed in \var{args}.
 203 \end{funcdesc}
 204
 205 \begin{funcdesc}{getargvalues}{frame}
 206   Get information about arguments passed into a particular frame.
 207   A tuple of four things is returned: \code{(\var{args},
 208     \var{varargs}, \var{varkw}, \var{locals})}.
 209   \var{args} is a list of the argument names (it may contain nested
 210   lists).
 211   \var{varargs} and \var{varkw} are the names of the \code{*} and
 212   \code{**} arguments or \code{None}.
 213   \var{locals} is the locals dictionary of the given frame.
 214 \end{funcdesc}
 215
 216 \begin{funcdesc}{formatargspec}{args\optional{, varargs, varkw, defaults,
 217       argformat, varargsformat, varkwformat, defaultformat}}
 218
 219   Format a pretty argument spec from the four values returned by
 220   \function{getargspec()}.  The other four arguments are the
 221   corresponding optional formatting functions that are called to turn
 222   names and values into strings.
 223 \end{funcdesc}
 224
 225 \begin{funcdesc}{formatargvalues}{args\optional{, varargs, varkw, locals,
 226       argformat, varargsformat, varkwformat, valueformat}}
 227   Format a pretty argument spec from the four values returned by
 228   \function{getargvalues()}.  The other four arguments are the
 229   corresponding optional formatting functions that are called to turn
 230   names and values into strings.
 231 \end{funcdesc}
 232
 233 \subsection{The interpreter stack
 234             \label{inspect-stack}}
 235
 236 When the following functions return ``frame records,'' each record
 237 is a tuple of six items: the frame object, the filename,
 238 the line number of the current line, the function name, a list of
 239 lines of context from the source code, and the index of the current
 240 line within that list.
 241 The optional \var{context} argument specifies the number of lines of
 242 context to return, which are centered around the current line.
 243
 244 \begin{funcdesc}{getouterframes}{frame\optional{, context}}
 245   Get a list of frame records for a frame and all higher (calling)
 246   frames.
 247 \end{funcdesc}
 248
 249 \begin{funcdesc}{getinnerframes}{traceback\optional{, context}}
 250   Get a list of frame records for a traceback's frame and all lower
 251   frames.
 252 \end{funcdesc}
 253
 254 \begin{funcdesc}{currentframe}{}
 255   Return the frame object for the caller's stack frame.
 256 \end{funcdesc}
 257
 258 \begin{funcdesc}{stack}{\optional{context}}
 259   Return a list of frame records for the stack above the caller's
 260   frame.
 261 \end{funcdesc}
 262
 263 \begin{funcdesc}{trace}{\optional{context}}
 264   Return a list of frame records for the stack below the current
 265   exception.
 266 \end{funcdesc}