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26.1. sys — System-specific parameters and functions

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26.3. __main__ — Top-level script environment

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26.2. __builtin__ — Built-in objects

This module provides direct access to all ‘built-in’ identifiers of Python; for example, is the full name for the built-in function open(). See chapter Built-in Objects.

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 =, ‘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):

# ...

As an 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.