The select module only allows lists, not any 
iterable.  While this may slightly increase efficiency 
for the select.select() function itself, for many 
applications passing select.select a sets.Set would 
probably be much more efficient (i.e., when things 
are being added/removed from the readable or 
writable lists quite often, the O(n) removal of lists 
would certainly be worse than the O(1) removal of 
sets.)