Lists of lists traversal

[Justin Sheehy]

"Benjamin Dixon" <beatle at arches.uga.edu> writes:

> Hello, I am new to Python and am trying to figure out how I can iterate
> over a list that I know to contain other lists of integers so that I can
> add up the individual lists inside the larger list.
> 
> I tried things like this:
> 
> Sum(input):
> 	for x in input:
> 		value = 0
> 		for y in input:
> 			value = value + y
> 	return y

Your description above doesn't give me a very clear idea of what you
are trying to do.  The following function, given a list of lists of
numbers, will return a list of their sums:

>>> def Sum(ls):
...   from operator import add
...   newls = []
...   for i in ls:
...     newls.append(reduce(add, i))
...   return newls
... 
>>> l = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
>>> Sum(l)
[6, 15, 24]

Perhaps from there you can find a way to solve whatever problem you
are trying to solve.

-Justin