"""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