Nested list comprehension with two lists

Question

I understand how the simple list comprehension works eg.:

[x*2 for x in range(5)] # returns [0,2,4,6,8]

and also I understand how the nested

Answer 1

List comprehensions are equivalent to for-loops. Therefore, [x + y for x in l2 for y in l1 ] would become:

new_list = []
for x in l2:
    for y in l1:
        new_list.append(x + y)

Whereas zip returns tuples containing one element from each list. Therefore [x + y for x,y in zip(l1,l2)] is equivalent to:

new_list = []
assert len(l1) == len(l2)
for index in xrange(len(l1)):
    new_list.append(l1[index] + l2[index])