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pythonposix

`ON_POSIX = 'posix' in sys.builtin_module_names` instruction meaning

I am new to python and I would like to know what this instruction is for:

ON_POSIX = 'posix' in sys.builtin_module_names

I know it might seem trivial to most of you but I could not find a clear explanation on the internet.

Thanks in advance for your help

Solution

  • From a high-level perspective you're checking if posix module is built-in the Python Interpreter ( meaning compiled into the Python interpreter itself).

    sys.builtin_module_names returns a tuple of strings giving the names of all modules that are compiled into this Python interpreter.

    If you take a look at the posix module :

    import posix
help(posix)

    You can see that this module is built-in :

    Help on built-in module posix:

NAME
    posix

FILE
    (built-in)

MODULE DOCS
    http://docs.python.org/library/posix

DESCRIPTION
    This module provides access to operating system functionality that is
    standardized by the C Standard and the POSIX standard (a thinly
    disguised Unix interface).  Refer to the library manual and
    corresponding Unix manual entries for more information on calls.

    By contrast you can do the same for os module:

    import os
help(os)

    As you can see os in not compiled into the Python Interpreter FILE: /usr/lib64/python2.7/os.py:

    Help on module os:

NAME
    os - OS routines for Mac, NT, or Posix depending on what system we're on.

FILE
    /usr/lib64/python2.7/os.py