cpython/Doc/library/__builtin__.rst

:mod:`__builtin__` --- Built-in objects
=======================================

.. module:: __builtin__
   :synopsis: The module that provides the built-in namespace.


This module provides direct access to all 'built-in' identifiers of Python; for
example, ``__builtin__.open`` is the full name for the built-in function
:func:`open`.  See chapter :ref:`builtin`.

This module is not normally accessed explicitly by most applications, but can be
useful in modules that provide objects with the same name as a built-in value,
but in which the built-in of that name is also needed.  For example, in a module
that wants to implement an :func:`open` function that wraps the built-in
:func:`open`, this module can be used directly::

   import __builtin__

   def open(path):
       f = __builtin__.open(path, 'r')
       return UpperCaser(f)

   class UpperCaser:
       '''Wrapper around a file that converts output to upper-case.'''

       def __init__(self, f):
           self._f = f

       def read(self, count=-1):
           return self._f.read(count).upper()

       # ...

.. impl-detail::

   Most modules have the name ``__builtins__`` (note the ``'s'``) made available
   as part of their globals.  The value of ``__builtins__`` is normally either
   this module or the value of this modules's :attr:`__dict__` attribute.  Since
   this is an implementation detail, it may not be used by alternate
   implementations of Python.