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

Answer 1

you can use zip():

In [16]: lis=[[1,2,3],
   ....:  [1,2,3]]

In [17]: map(sum,zip(*lis))
Out[17]: [2, 4, 6]

or with a simple for loops:

In [25]: for i in xrange(len(lis[0])):
    summ=0
    for x in lis:
        summ+=x[i]
    print summ
   ....:     
2
4
6