"""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