What is a Python 3 construct?

Question

Python

Please sort it out: what is happening in this code fragment:
m = [[0 for x in s2 + 't'] for c in s1 + 't']
s1 and s2 are lines

Answer 1

This code builds a matrix (list of lists) of zeros, size len(s2) + 1 by len(s1) + 1 (where +1 is +'t'). It's just a short for for to create lists.