16.4. "dummy_threading" –  可直接替代 "threading" 模块。
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**源代码：** Lib/dummy_threading.py

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This module provides a duplicate interface to the "threading" module.
It is meant to be imported when the "thread" module is not provided on
a platform.

Suggested usage is:

   try:
       import threading as _threading
   except ImportError:
       import dummy_threading as _threading

Be careful to not use this module where deadlock might occur from a
thread being created that blocks waiting for another thread to be
created.  This  often occurs with blocking I/O.
