looping over more than one list

[Tim Chase]

> def lowest(s1,s2):
>     s = ""
>     for i in xrange(len(s1)):
>         s += lowerChar(s1[i],s2[i])
>     return s
> 
> this seems unpythonic, compared to something like:
> 
> def lowest(s1,s2):
>     s = ""
>     for c1,c2 in s1,s2:
>         s += lowerChar(c1,c2)
>     return s

If I understand correctly, something like

	for c1,c2 in zip(s1,s2):

is what you're looking for.  It will gracefully stop when it 
reaches the end of the shortest input. (in your indexed 
example above, if s2 is shorter than s1, it will likely 
throw an out-of-bounds exception)

For your example, I'd use

def lowest(s1,s2):
   return ''.join([lowerChar(c1,c2) for c1,c2 in zip(s1,s2)])

which seems to do what you describe (I understand that 
appending to strings is an inefficient operation and is 
better done with a join like this)

-tkc