None module reference

[Stefan Seefeld]

hello,

I'v run into a bug that I find hard to understand:

In a python module of mine I import system modules
('sys', say) and then use them from within some functions.

However, during program termination I'm calling
one such function and the module reference ('sys')
is 'None' !

What does that mean ? Have those modules already
been unloaded ? If so, why, given that my
current module still references them ?

Any help is highly appreciated,

		Stefan