from __future__ import division
from py_stringmatching import utils
from py_stringmatching.similarity_measure.cython_levenshtein import levenshtein
from py_stringmatching.similarity_measure.sequence_similarity_measure import \
SequenceSimilarityMeasure
[docs]class Levenshtein(SequenceSimilarityMeasure):
"""Computes Levenshtein measure (also known as edit distance).
Levenshtein distance computes the minimum cost of transforming one string into the other. Transforming a string
is carried out using a sequence of the following operators: delete a character, insert a character, and
substitute one character for another.
"""
def __init__(self):
super(Levenshtein, self).__init__()
[docs] def get_raw_score(self, string1, string2):
"""Computes the raw Levenshtein distance between two strings.
Args:
string1,string2 (str): Input strings.
Returns:
Levenshtein distance (int).
Raises:
TypeError : If the inputs are not strings.
Examples:
>>> lev = Levenshtein()
>>> lev.get_raw_score('a', '')
1
>>> lev.get_raw_score('example', 'samples')
3
>>> lev.get_raw_score('levenshtein', 'frankenstein')
6
"""
# input validations
utils.sim_check_for_none(string1, string2)
# convert input to unicode.
string1 = utils.convert_to_unicode(string1)
string2 = utils.convert_to_unicode(string2)
utils.tok_check_for_string_input(string1, string2)
if utils.sim_check_for_exact_match(string1, string2):
return 0.0
return levenshtein(string1, string2)
[docs] def get_sim_score(self, string1, string2):
"""Computes the normalized Levenshtein similarity score between two strings.
Args:
string1,string2 (str): Input strings.
Returns:
Normalized Levenshtein similarity (float).
Raises:
TypeError : If the inputs are not strings.
Examples:
>>> lev = Levenshtein()
>>> lev.get_sim_score('a', '')
0.0
>>> lev.get_sim_score('example', 'samples')
0.5714285714285714
>>> lev.get_sim_score('levenshtein', 'frankenstein')
0.5
"""
# convert input strings to unicode.
string1 = utils.convert_to_unicode(string1)
string2 = utils.convert_to_unicode(string2)
raw_score = self.get_raw_score(string1, string2)
max_len = max(len(string1), len(string2))
if max_len == 0:
return 1.0
return 1 - (raw_score / max_len)