python-string-similarity/similarity/levenshtein.py

from .string_distance import MetricStringDistance


class Levenshtein(MetricStringDistance):

    def distance(self, s0, s1):
        if s0 is None:
            raise TypeError("Argument s0 is NoneType.")
        if s1 is None:
            raise TypeError("Argument s1 is NoneType.")
        if s0 == s1:
            return 0.0
        if len(s0) == 0:
            return len(s1)
        if len(s1) == 0:
            return len(s1)

        v0 = [0] * (len(s1) + 1)
        v1 = [0] * (len(s1) + 1)

        for i in range(len(v0)):
            v0[i] = i

        for i in range(len(s0)):
            v1[0] = i + 1
            for j in range(len(s1)):
                cost = 1
                if s0[i] == s1[j]:
                    cost = 0
                v1[j + 1] = min(v1[j] + 1, v0[j + 1] + 1, v0[j] + cost)
            v0, v1 = v1, v0

        return v0[len(s1)]