This module has been removed in Python 3.x.
Raised if the observer callback cannot be installed, for example because the current thread does not have a run loop.
Install an observer callback in the event loop (CFRunLoop) for the current thread, that will lock and unlock the Global Interpreter Lock (GIL) at appropriate times, allowing other Python threads to run while the event loop is idle.
Availability: OSX 10.1 or later.
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