Manual string 'in' function doesn't work if substring is at the end of the word

Question

I'm trying to manually code the python string in function for an assignment. Using this code, where s is the string and t is the substring I am trying to find:

def test(s, t):
    stidx = 0
    while stidx < len(s):
        idx = 0
        for i in s[stidx:]:
            if idx < len(t):
                if t[idx] == i:
                    idx += 1
                    continue
                else:
                    break
            if idx == len(t):
                return True
        stidx += 1
    return False

The above code works, except when I am checking a substring at the very end of the word (e.g. s = 'happy' and t = 'py'). If I add an arbitrary character to the end of s, it works. Why is this?

Sometimes walking through your code on paper helps or you can watch it execute at http://www.pythontutor.com/visualize.html#mode=edit. — wwii, Sep 29 '19 at 23:54

score 0 · Answer 1 · answered Sep 30 '19 at 01:41

maybe?

def test(s, t):
    """
    :param s:   exp: happy
    :param t:   exp: py
    :return:
    """
    tmp = result = 0
    t_len = len(t)
    while tmp <= len(s)-t_len:
        if s[tmp: tmp+t_len] == t:
            result = 1
            break
        else:
            tmp += 1
            continue

    return bool(result)

Manual string 'in' function doesn't work if substring is at the end of the word

1 Answers1