fix some issues in hamming distance

CHANGELOG.md

@@ -9,6 +9,9 @@
 
 #### Fixed
 - fuzz.partial_ratio_alignment ignored the score_cutoff
+- fix implementation of Hamming.normalized_similarity
+- fix default score_cutoff of Hamming.similarity
+- fix implementation of LCSseq.distance when used in the process module
 
 ### [2.0.15] - 2022-06-24
 #### Fixed

extern/rapidfuzz-cpp

@@ -1 +1 @@
-Subproject commit db5ac864bcb2890556c0e5b3c0a13335e65ac3e3
+Subproject commit 13d7c7751b23dd2ef1efb340572661972941675c

rapidfuzz/distance/Hamming_cpp.pyx

@@ -103,7 +103,7 @@ def similarity(s1, s2, *, processor=None, score_cutoff=None):
     ValueError
         If s1 and s2 have a different length
     """
-    cdef int64_t c_score_cutoff = INT64_MAX if score_cutoff is None else score_cutoff
+    cdef int64_t c_score_cutoff = 0 if score_cutoff is None else score_cutoff
     cdef RF_StringWrapper s1_proc, s2_proc
 
     if c_score_cutoff < 0:
@@ -187,7 +187,7 @@ def normalized_similarity(s1, s2, *, processor=None, score_cutoff=None):
         raise ValueError("score_cutoff has to be >= 0")
 
     preprocess_strings(s1, s2, processor, &s1_proc, &s2_proc, None)
-    return hamming_normalized_distance_func(s1_proc.string, s2_proc.string, c_score_cutoff)
+    return hamming_normalized_similarity_func(s1_proc.string, s2_proc.string, c_score_cutoff)
 
 
 cdef bool NoKwargsInit(RF_Kwargs* self, dict kwargs) except False:

tests/distance/test_Hamming.py

@@ -0,0 +1,83 @@
+import unittest
+
+from rapidfuzz.distance import Hamming_cpp, Hamming_py
+
+
+def isclose(a, b, rel_tol=1e-09, abs_tol=0.0):
+    return abs(a - b) <= max(rel_tol * max(abs(a), abs(b)), abs_tol)
+
+
+class Hamming:
+    @staticmethod
+    def distance(*args, **kwargs):
+        dist1 = Hamming_cpp.distance(*args, **kwargs)
+        dist2 = Hamming_py.distance(*args, **kwargs)
+        assert dist1 == dist2
+        return dist1
+
+    @staticmethod
+    def similarity(*args, **kwargs):
+        dist1 = Hamming_cpp.similarity(*args, **kwargs)
+        dist2 = Hamming_py.similarity(*args, **kwargs)
+        assert dist1 == dist2
+        return dist1
+
+    @staticmethod
+    def normalized_distance(*args, **kwargs):
+        dist1 = Hamming_cpp.normalized_distance(*args, **kwargs)
+        dist2 = Hamming_py.normalized_distance(*args, **kwargs)
+        assert isclose(dist1, dist2)
+        return dist1
+
+    @staticmethod
+    def normalized_similarity(*args, **kwargs):
+        dist1 = Hamming_cpp.normalized_similarity(*args, **kwargs)
+        dist2 = Hamming_py.normalized_similarity(*args, **kwargs)
+        assert isclose(dist1, dist2)
+        return dist1
+
+
+def test_empty_string():
+    """
+    when both strings are empty this is a perfect match
+    """
+    assert Hamming.distance("", "") == 0
+    assert Hamming.similarity("", "") == 0
+    assert Hamming.normalized_distance("", "") == 0.0
+    assert Hamming.normalized_similarity("", "") == 1.0
+
+
+def test_similar_strings():
+    """
+    Test similar strings
+    """
+    assert Hamming.distance("test", "test") == 0
+    assert Hamming.similarity("test", "test") == 4
+    assert Hamming.normalized_distance("test", "test") == 0
+    assert Hamming.normalized_similarity("test", "test") == 1.0
+
+
+def test_different_strings():
+    """
+    Test completly different strings
+    """
+    assert Hamming.distance("aaaa", "bbbb") == 4
+    assert Hamming.similarity("aaaa", "bbbb") == 0
+    assert Hamming.normalized_distance("aaaa", "bbbb") == 1.0
+    assert Hamming.normalized_similarity("aaaa", "bbbb") == 0.0
+
+
+def test_score_cutoff():
+    """
+    test whether score_cutoff works correctly
+    """
+    assert Hamming.distance("South Korea", "North Korea") == 2
+    assert Hamming.distance("South Korea", "North Korea", score_cutoff=4) == 2
+    assert Hamming.distance("South Korea", "North Korea", score_cutoff=3) == 2
+    assert Hamming.distance("South Korea", "North Korea", score_cutoff=2) == 2
+    assert Hamming.distance("South Korea", "North Korea", score_cutoff=1) == 2
+    assert Hamming.distance("South Korea", "North Korea", score_cutoff=0) == 1
+
+
+if __name__ == "__main__":
+    unittest.main()