28.3. "__builtin__" — Built-in objects
**************************************

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 "open()".  See 内置函数 and Built-in Constants for
documentation.

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 "open()"
function that wraps the built-in "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()

       # ...

**CPython implementation 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 "__dict__" attribute.  Since this is an
implementation detail, it may not be used by alternate implementations
of Python.
