indexof.py

def indexof(fromstr, substr):
    f = s = 0

    while f < len(fromstr):
        if fromstr[f] == substr[s]:
            if s == len(substr) - 1:
                return f - s

            s += 1
        else:
            s = 0

        f += 1

    return -1


assert indexof('something', 'else') == -1
assert indexof('something', 's') == 0
assert indexof('something', 'g') == 8
assert indexof('something', 'some') == 0
assert indexof('something', 'thing') == 4