Finds common factor between two unorganized lists

factor.py

#!/usr/bin/env python
def answer(x, y):
    
    sum_x, sum_y = sum(x), sum(y)
    before = max(x, y)
    after = min(x, y)
    if after == 0: 
        return 100
    return int(round(abs((sum(before) / sum(after) - 1)) * 100))