Doc/lib/libbltin.tex

   1 \section{\module{__builtin__} ---
   2          Built-in objects}
   3
   4 \declaremodule[builtin]{builtin}{__builtin__}
   5 \modulesynopsis{The module that provides the built-in namespace.}
   6
   7
   8 This module provides direct access to all `built-in' identifiers of
   9 Python; for example, \code{__builtin__.open} is the full name for the
  10 built-in function \function{open()}.  See chapter~\ref{builtin},
  11 ``Built-in Objects.''
  12
  13 This module is not normally accessed explicitly by most applications,
  14 but can be useful in modules that provide objects with the same name
  15 as a built-in value, but in which the built-in of that name is also
  16 needed.  For example, in a module that wants to implement an
  17 \function{open()} function that wraps the built-in \function{open()},
  18 this module can be used directly:
  19
  20 \begin{verbatim}
  21 import __builtin__
  22
  23 def open(path):
  24     f = __builtin__.open(path, 'r')
  25     return UpperCaser(f)
  26
  27 class UpperCaser:
  28     '''Wrapper around a file that converts output to upper-case.'''
  29
  30     def __init__(self, f):
  31         self._f = f
  32
  33     def read(self, count=-1):
  34         return self._f.read(count).upper()
  35
  36     # ...
  37 \end{verbatim}
  38
  39 As an implementation detail, most modules have the name
  40 \code{__builtins__} (note the \character{s}) made available as part of
  41 their globals.  The value of \code{__builtins__} is normally either
  42 this module or the value of this modules's \member{__dict__}
  43 attribute.  Since this is an implementation detail, it may not be used
  44 by alternate implementations of Python.