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 Built-in Functions 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.