"""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.

"""
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