Sum numbers in a list of lists in Python 2.7

Question

I've got a list of lists in Python 2.7 with numbers in strings:

[['1', '2'], ['3'], ['4', '5', '6']]

How could I sum all the numbers in these lists?

One way would be to flatten the list, parse the elements and calculate the sum. What have you tried so far? — sam, Nov 06 '15 at 13:00
`sum([int(i) for s in a for i in s])` where `a` is your list — tmdavison, Nov 06 '15 at 13:07
@PeterWood its an alternative that works? unless you have a particular reason why not? KevenGuan - fair enough — tmdavison, Nov 06 '15 at 13:11

Avión · Answer 1 · 2015-11-06T13:04:32.047

3

You have first chain all the lists, then convert them to int using map and finally sum them.

import itertools
m =  [['1', '2'], ['3'], ['4', '5', '6']]
print sum(map(int, list(itertools.chain(*m))))

Output:

edited Nov 06 '15 at 13:04

answered Nov 06 '15 at 13:03

Avión

score 3 · Answer 2 · answered Nov 06 '15 at 13:09

3

As an alternate solution to chaining them you could use list comprehension and convert each element to an int and then sum the new list

l = [['1', '2'], ['3'], ['4', '5', '6']]

print sum([int(j) for i in l for j in i])

21

answered Nov 06 '15 at 13:09

SirParselot

2 Answers2