Strictly 'local' threads in Python?

[Robert Yodlowski]

I need to control several concurrently running, independent sequences of
activities from Python functions. Up to now I've been using the standard
Python threading module with fine results.

Now, I need to be able to do something similar but embedded in a different
application that "does not support threading". I've tried embedding Python
with the standard threading module but the application crashes immediately
when I try to run it.

The only reason I've used threads is to avoid the need to 'manually' keep
track of where each sequence is executing as control is passed around from
one sequence to another. I explicitly 'hop' from thread to thread so only a
single thread is active at any given instant.

It seems to me that this limited form of threading could be accomplished
strictly locally within the Python interpreter without any need to include
or use the OS's threading facility.

Can this be done?
Has anyone done it?
Any advice would be appreciated.

...Bob