How can I sum a column of a list?

Question

I have a Python array, like so:

[[1,2,3],
 [1,2,3]]

I can add the row by doing sum(array[i]), how can I sum a column, using a double for loop?

I.E. for the first column, I could get 2, then 4, then 6.

Answer 1

Using a for loop (in a generator expression):

data = [[1,2,3],
        [1,2,3]]

column = 1
print(sum(row[column] for row in data))  # -> 4

Answer 2

Try this:

a = [[1,2,3],
     [1,2,3]]

print [sum(x) for x in zip(*a)]

zip function description