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Mon Aug 16 05:38:30 CEST 2004 · https://mail.python.org/pipermail/python-dev/2004-August/047854.html

>>>>> "Raymond" == Raymond Hettinger <python at rcn.com> writes:

    Raymond> Threading is a technique for decoupling tasks which are
    Raymond> not sequentially dependent and creating the illusion of
    Raymond> concurrency.

All simultaneity is an illusion, but the concurrency of Python threads
is not. <wink>

    Raymond> Also, multiple processors cannot boost performance
    Raymond> because Python's Global Interpreter Lock (GIL) precludes
    Raymond> more than one thread from running in the interpreter at
    Raymond> the same time (this was done to simplify re-entrancy
    Raymond> issues).

This confused me because "running" is ambiguous.  How about something
like:

    The Python interpreter itself is not fully reentrant, so threading
    is accomplished by interleaving the execution of Python code from
    different threads.  Thus, use of multiple processors cannot boost
    performance of threaded Python code, because a single instance of
    the interpreter can only execute code on one processor at a time.

(Season to taste, fix technical inaccuracies.)  I see no reason to
mention the GIL, an implementation detail, at all.

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[Python-Dev] Threading in the Standard Library Tour Part II