It's simple: if you want to modify the data structure after it has been created, use lists, otherwise tuples.
Tuples are much more memory efficient, so your program will consume less memory and probably run faster. So preferably use tuples. However with tuples you can't do: t[0] = 'new value' t.append('new value') These statements are possible with lists. Stani -- SPE - Stani's Python Editor (http://pythonide.stani.be) -- http://mail.python.org/mailman/listinfo/python-list