[Zope] Newbie: need a simple example of external method

Hi, I just subscribed to the mailing list, and in less than one day I got 60 messages, wow! This list surely is active. Can anyone give to me a simple example of a DTML document calling an external method? I mean, if I have a Python program myprogram.py: def myfunc(x): return 2*x; How do I proceed to use it in DTML, and how do I place it in the external methods folder? regards, Hung Jung