splitting lines, need to add element of same kind

[deanhystad]

A dictionary makes this easy.

source = [
    '5, cat',
    '3, dog',
    '1, cat',
    '1, fish',
    '2, dog',
    '3, bird']

animals = {}

for line in source:
    count, animal = line.split(',')
    animals[animal] = animals.get(animal, 0) + int(count)

print(animals)

Output:
{' cat': 6, ' dog': 5, ' fish': 1, ' bird': 3}

If you only want to count certain animals:

source = [
    '5, cat',
    '3, dog',
    '1, cat',
    '1, fish',
    '2, dog',
    '3, bird']

animals = {'cat':0, 'dog':0}

for line in source:
    count, animal = line.split(',')
    if animal in animals:
        animals[animal] += int(count)

print(animals)

Output:
{'cat': 0, 'dog': 0}