The simplest way to concatenate list1 and list2:
merged = list1 + list2
zip returns a list of tuples, where the i-th tuple contains the i-th element from each of the argument sequences or iterables:
alist = ['a1', 'a2', 'a3']
blist = ['b1', 'b2', 'b3']
for a, b in zip(alist, blist):...