[Zope] Brute force?

I tried to get an external method to import a function from another python file which did't work if that other file was in the Extensions directory, too. So I tried out where it would work and ended up with my import file in zope/lib/python where it also was byte-compiled nicely after the next zope restart. But: this somehow felt to me like brute force. Where would one normally put a file to import from? Is there a strategy that I missed? Documentation? Ragnar