"""Faux ``threading`` version using ``dummy_thread`` instead of ``thread``. The module ``_dummy_threading`` is added to ``sys.modules`` in orderto not have ``threading`` considered imported.  Had ``threading`` beendirectly imported it would have made all subsequent imports succeedregardless 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 = Falseholding_threading = Falseholding__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