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

[x + y for x in l2 for y in l1 ]

is equivalent to :

lis = []
for x in l:
   for y in l1:
      lis.append(x+y)

So for every element of l you're iterating l2 again and again, as l has 3 elements and l1 has elements so total loops equal 9(len(l)*len(l1)).