is checks for identity. [] and [] are two different (but equivalent) lists. If you want to check if both the lists are empty you can use their truth value (false for empty strings, collections, and zeros).
if not ([] and []):
print 'Spanish Inquisition'
the only time that is is guaranteed to return True is for singletons such as None. Like the Highlander, there can be only one instance of None in your program - every time you return None it's the very same "thing" as the none referred to if you type print None.
[], OTOH, is not guaranteed to be anything except an empty list and evaluate to False in a boolean context.
