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

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

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

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directly imported it would have made all subsequent imports succeed

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

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"""

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from sys import modules as sys_modules

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import dummy_thread

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

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holding_thread = False

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holding_threading = False

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holding__threading_local = False

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try:

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

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

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# ``threading`` below.

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if 'thread' in sys_modules:

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held_thread = sys_modules['thread']

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holding_thread = True

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

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

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

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if 'threading' in sys_modules:

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

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

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# already imported before deleting it.

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held_threading = sys_modules['threading']

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holding_threading = True

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del sys_modules['threading']

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if '_threading_local' in sys_modules:

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

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

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# already imported before deleting it.

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held__threading_local = sys_modules['_threading_local']

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holding__threading_local = True

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del sys_modules['_threading_local']

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import threading

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

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

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del sys_modules['threading']

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

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del sys_modules['_threading_local']

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from _dummy_threading import *

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from _dummy_threading import __all__

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finally:

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

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if holding_threading:

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sys_modules['threading'] = held_threading

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del held_threading

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del holding_threading

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

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if holding__threading_local:

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sys_modules['_threading_local'] = held__threading_local

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del held__threading_local

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del holding__threading_local

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

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if holding_thread:

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sys_modules['thread'] = held_thread

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del held_thread

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else:

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del sys_modules['thread']

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del holding_thread

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del dummy_thread

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del sys_modules

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