Thread programming (not necessarily of the Python flavor)
has some interesting properties. Truly pre-emptive systems
are scary in that a program may work 99.9999% of the
time and fail .0001% of the time. This is because the
order that program instructions are executed may vary with
each invocation (depending on the thread scheduling algorithm).
Unless properly synchronized, very short (in time) windows may
exist where the program is in an invalid state.
Just don't expect robustness unless you are really sure of
what you are doing.
Lack of true thread support is my ONLY disappointment with Python.
-Richard Walker