Global Interpreter Lock

[Tomas Christiansen]

Excaclty HOW global is the global interpreter lock?

I know that it isn't global in the meaning "the hole world" (imagine that!),
but is it global only to each task/job/python interpreter instance (running
one or more threads) or is it global to the user or the computer or...?

In other words, what is the impact of the global interpreter lock if...
 1. If user A has two different python programs running?
 2. If user A is running a python program and user B is running one as well?
 3. Does the OS (Linux or Windows) make a difference to the impact of the
global interpreter lock?

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Tomas