python-string-similarity/strsim/levenshtein.py

# Copyright (c) 2018 luozhouyang
#
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# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# SOFTWARE.

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)]