1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
"""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