List comprehension is a compact way to process all or part of the elements in a sequence and return a list with the results. where result =[‘{ :#04x }’. format(x) for x in range(256) if x % 2 == 0] generates a list of strings containing even hex numbers (0x..) in the range from 0 to 255. The if clause is optional. If omitted, all elements in range(256) are processed.