How to sum a 2d array in Python?

Question

I want to sum a 2 dimensional array in python:

Here is what I have:

def sum1(input):
    sum = 0
    for row in range (len(input)-1):
        for col in range(len(input[0])-1):
            sum = sum + input[row][col]

    return sum


print sum1([[1, 2],[3, 4],[5, 6]])

It displays 4 instead of 21 (1+2+3+4+5+6 = 21). Where is my mistake?

Answer 1

I think this is better:

 >>> x=[[1, 2],[3, 4],[5, 6]]                                                   
>>> sum(sum(x,[]))                                                             
21

Answer 2

You could rewrite that function as,

def sum1(input):
    return sum(map(sum, input))

Basically, map(sum, input) will return a list with the sums across all your rows, then, the outer most sum will add up that list.

Example:

>>> a=[[1,2],[3,4]]
>>> sum(map(sum, a))
10