rosalind Finding a Motif in DNA

import re

string = '''ACATTTAACGCTTAACGCTTAACGCGCAGTGTGTTAACGCTTAACGC'''
sub = '''TTAACGCTT'''

def find_all(string, sub):
    start = 0
    pos = []
    while True:
        start = string.find(sub, start)
        if start == -1:
            return pos
        pos.append(int(start)+1)
        start += 1

print(find_all(string,sub))