Sum lists with different lengths

Question

What's the best way to sum two or more lists even if they have different lengths?

For example I have:

lists = [[1, 2], [0, 3, 4], [5]]

and the result should be:

result = [6, 5, 4]

Answer 1

You can use itertools.izip_longest(), and use a fillvalue equal to 0

In [6]: [sum(x) for x in itertools.izip_longest(*lists, fillvalue=0)]
Out[6]: [6, 5, 4]

for Python < 2.6:

In [27]: ml = max(map(len, lists))

In [28]: ml       #length of the longest list in lists
Out[28]: 3

In [29]: [sum(x) for x in zip(*map(lambda x:x+[0]*ml if len(x)<ml else x, lists))]
Out[29]: [6, 5, 4]

Answer 2

#You can do the same without using predefined header files.
def sumlists(a,b,c):
    sumlist = []
    while(len(a)!=len(b) or len(a)!=len(c)):
        if len(a)>len(b):
            b.append(0)
        if len(a)>len(c):
            c.append(0)
        elif len(b)>len(a):
            a.append(0)
        if len(b)>len(c):
             c.append(0)
        elif len(c)>len(a):
            a.append(0)
        if len(c)>len(b):
             b.append(0)
    for i,j,k in zip(a,b,c):
         sumlist.append(i+j+k)
    return sumlist
 print(sumlists([1,2],[0,3,4],[5]))