"""Faux ``threading`` version using ``dummy_thread`` instead of ``thread``.

The module ``_dummy_threading`` is added to ``sys.modules`` in order

to not have ``threading`` considered imported.  Had ``threading`` been

directly imported it would have made all subsequent imports succeed

regardless of whether ``thread`` was available which is not desired.

:Author: Brett Cannon

:Contact: brett@python.org

XXX: Try to get rid of ``_dummy_threading``.

"""

from sys import modules as sys_modules

import dummy_thread

# Declaring now so as to not have to nest ``try``s to get proper clean-up.

holding_thread = False

holding_threading = False

holding__threading_local = False

try:

    # Could have checked if ``thread`` was not in sys.modules and gone

    # a different route, but decided to mirror technique used with

    # ``threading`` below.

    if 'thread' in sys_modules:

        held_thread = sys_modules['thread']

        holding_thread = True

    # Must have some module named ``thread`` that implements its API

    # in order to initially import ``threading``.

    sys_modules['thread'] = sys_modules['dummy_thread']

    if 'threading' in sys_modules:

        # If ``threading`` is already imported, might as well prevent

        # trying to import it more than needed by saving it if it is

        # already imported before deleting it.

        held_threading = sys_modules['threading']

        holding_threading = True

        del sys_modules['threading']

    if '_threading_local' in sys_modules:

        # If ``_threading_local`` is already imported, might as well prevent

        # trying to import it more than needed by saving it if it is

        # already imported before deleting it.

        held__threading_local = sys_modules['_threading_local']

        holding__threading_local = True

        del sys_modules['_threading_local']

    import threading

    # Need a copy of the code kept somewhere...

    sys_modules['_dummy_threading'] = sys_modules['threading']

    del sys_modules['threading']

    sys_modules['_dummy__threading_local'] = sys_modules['_threading_local']

    del sys_modules['_threading_local']

    from _dummy_threading import *

    from _dummy_threading import __all__

finally:

    # Put back ``threading`` if we overwrote earlier

    if holding_threading:

        sys_modules['threading'] = held_threading

        del held_threading

    del holding_threading

    # Put back ``_threading_local`` if we overwrote earlier

    if holding__threading_local:

        sys_modules['_threading_local'] = held__threading_local

        del held__threading_local

    del holding__threading_local

    # Put back ``thread`` if we overwrote, else del the entry we made

    if holding_thread:

        sys_modules['thread'] = held_thread

        del held_thread

    else:

        del sys_modules['thread']

    del holding_thread

    del dummy_thread

    del sys_modules