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

     2 

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

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

     5 directly imported it would have made all subsequent imports succeed

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

     7 

     8 :Author: Brett Cannon

     9 :Contact: brett@python.org

    10 

    11 XXX: Try to get rid of ``_dummy_threading``.

    12 

    13 """

    14 from sys import modules as sys_modules

    15 

    16 import dummy_thread

    17 

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

    19 holding_thread = False

    20 holding_threading = False

    21 holding__threading_local = False

    22 

    23 try:

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

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

    26     # ``threading`` below.

    27     if 'thread' in sys_modules:

    28         held_thread = sys_modules['thread']

    29         holding_thread = True

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

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

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

    33 

    34     if 'threading' in sys_modules:

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

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

    37         # already imported before deleting it.

    38         held_threading = sys_modules['threading']

    39         holding_threading = True

    40         del sys_modules['threading']

    41 

    42     if '_threading_local' in sys_modules:

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

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

    45         # already imported before deleting it.

    46         held__threading_local = sys_modules['_threading_local']

    47         holding__threading_local = True

    48         del sys_modules['_threading_local']

    49 

    50     import threading

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

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

    53     del sys_modules['threading']

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

    55     del sys_modules['_threading_local']

    56     from _dummy_threading import *

    57     from _dummy_threading import __all__

    58 

    59 finally:

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

    61 

    62     if holding_threading:

    63         sys_modules['threading'] = held_threading

    64         del held_threading

    65     del holding_threading

    66 

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

    68 

    69     if holding__threading_local:

    70         sys_modules['_threading_local'] = held__threading_local

    71         del held__threading_local

    72     del holding__threading_local

    73 

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

    75     if holding_thread:

    76         sys_modules['thread'] = held_thread

    77         del held_thread

    78     else:

    79         del sys_modules['thread']

    80     del holding_thread

    81 

    82     del dummy_thread

    83     del sys_modules