Sift4 in python

sift4.py

"""
Based on: https://gist.github.com/lbenedix/8275d01c2289a7a20d2c6c27ee8ae68e

Moved an if block and added a double empty string check for input validation

"""

def sift4_simple(s1, s2, max_offset=5):
    """

    :param s1: string to compare
    :param s2: string to compare
    :param max_offset: number of characters to search for matching letters
    :return: edit distance
    """
    if len(s1) == 0:
        if len(s2) == 0:
            return 0
        return len(s2)
    elif len(s2) == 0:
        return len(s1)

    l1 = len(s1)
    l2 = len(s2)

    c1 = 0  # cursor for s1
    c2 = 0  # cursor for s1
    lcss = 0  # longest common subsequence
    local_cs = 0  # local common subsequence

    while c1 < l1 and c2 < l2:
        if s1[c1] == s2[c2]:
            local_cs += 1
        else:
            lcss += local_cs
            local_cs = 0
            if c1 != c2:
                c1 = c2 = max(c1, c2)
            for i in range(max_offset):
                if c1 + i >= l1 or c2 + i >= l2:
                    break
                if len(s1) > c1 + i and s1[c1 + i] == s2[c2]:
                    c1 += i
                    local_cs += 1
                    break
                if len(s2) > c1 + i and s1[c1] == s2[c2 + i]:
                    c2 += i
                    local_cs += 1
                    break
        c1 += 1
        c2 += 1
    lcss += local_cs
    return round(max(l1, l2) - lcss)