Python implementation of exact-matching Bitap

bitap.py

def bitap_search(text, pattern):
    """
    Returns position of pattern in text or -1 if it wasn't found.
    text and pattern are strings.

    >>> bitap_search("test text", "tex")
    5

    >>> bitap_search("test text", "z")
    -1
    """
    m = len(pattern)

    if m == 0:
        return 0

    R = [False] * (m + 1)
    R[0] = True

    i = 0
    while i < len(text):
        k = m
        while k >= 1:
          R[k] = R[k - 1] and (text[i] == pattern[k-1])
          k -= 1

        # R[m] is the last element in R. If it's True, that means the entire pattern matched and we can return its position in the text.
        if R[m]:
            # i is now at the end of the pattern. Subtracting (m-1) puts us at the start of the pattern in text.
            return i - m + 1

        i += 1

    return -1