Python-сообщество

list(map(sum, itertools.zip_longest([1,2,3], [4,5], fillvalue=0)))

def sum_list_elements(la, lb):
    """Сложить списки одинаковой или разной длины поэлементно."""
    shortest, longest = la, lb
    if len(shortest) > len(longest):
        shortest, longest = longest, shortest
    shortest_extended = shortest + [0] * (len(longest) - len(shortest))
    return [i + j for i, j in zip(shortest_extended, longest)]

import itertools

if python_v_3:
    zip_extended = itertools.zip_longest
elif python_v_2:
    zip_extended = itertools.izip_longest

list(map(sum, zip_extended(la, lb, fillvalue=0)))

try:
    from itertools import izip_longest as zip_longest
except ImportError:
    from itertools import zip_longest