Python double iteration

Question

What is the pythonic way of iterating simultaneously over two lists?

Suppose I want to compare two files line by line (compare each ith line in one file

Answer 1

In lockstep (for Python ≥3):

for line1, line2 in zip(file1, file2):
   # etc.

As a "2D array":

for line1 in file1:
   for line2 in file2:
     # etc.
   # you may need to rewind file2 to the beginning.