Sum numbers by letter in list of tuples

Question

I have a list of tuples:

[ (\'A\',100), (\'B\',50), (\'A\',50), (\'B\',20), (\'C\',10) ]

I am trying to sum up all numbers that have the s

Answer 1

Try this:

a = [('A',100), ('B',50), ('A',50), ('B',20), ('C',10) ]

letters = set([s[0] for s in a])

new_a = []
for l in letters:
    nums = [s[1] for s in a if s[0] == l]
    new_a.append((l, sum(nums)))

print new_a    

Results:

[('A', 150), ('C', 10), ('B', 70)]