bpo-40394 - difflib.SequenceMatched.find_longest_match default args (GH-19742)

* bpo-40394 - difflib.SequenceMatched.find_longest_match default args

Added default args to find_longest_match, as well as related tests.

1 files changed, 47 insertions, 1 deletions

diff --git a/Lib/test/test_difflib.py b/Lib/test/test_difflib.py
index 5e2ca1a..42ac1fd 100644
--- a/Lib/test/test_difflib.py
+++ b/Lib/test/test_difflib.py
@@ -501,12 +501,58 @@ class TestJunkAPIs(unittest.TestCase):
         for char in ['a', '#', '\n', '\f', '\r', '\v']:
             self.assertFalse(difflib.IS_CHARACTER_JUNK(char), repr(char))
 
+class TestFindLongest(unittest.TestCase):
+    def longer_match_exists(self, a, b, n):
+        return any(b_part in a for b_part in
+                   [b[i:i + n + 1] for i in range(0, len(b) - n - 1)])
+
+    def test_default_args(self):
+        a = 'foo bar'
+        b = 'foo baz bar'
+        sm = difflib.SequenceMatcher(a=a, b=b)
+        match = sm.find_longest_match()
+        self.assertEqual(match.a, 0)
+        self.assertEqual(match.b, 0)
+        self.assertEqual(match.size, 6)
+        self.assertEqual(a[match.a: match.a + match.size],
+                         b[match.b: match.b + match.size])
+        self.assertFalse(self.longer_match_exists(a, b, match.size))
+
+        match = sm.find_longest_match(alo=2, blo=4)
+        self.assertEqual(match.a, 3)
+        self.assertEqual(match.b, 7)
+        self.assertEqual(match.size, 4)
+        self.assertEqual(a[match.a: match.a + match.size],
+                         b[match.b: match.b + match.size])
+        self.assertFalse(self.longer_match_exists(a[2:], b[4:], match.size))
+
+        match = sm.find_longest_match(bhi=5, blo=1)
+        self.assertEqual(match.a, 1)
+        self.assertEqual(match.b, 1)
+        self.assertEqual(match.size, 4)
+        self.assertEqual(a[match.a: match.a + match.size],
+                         b[match.b: match.b + match.size])
+        self.assertFalse(self.longer_match_exists(a, b[1:5], match.size))
+
+    def test_longest_match_with_popular_chars(self):
+        a = 'dabcd'
+        b = 'd'*100 + 'abc' + 'd'*100  # length over 200 so popular used
+        sm = difflib.SequenceMatcher(a=a, b=b)
+        match = sm.find_longest_match(0, len(a), 0, len(b))
+        self.assertEqual(match.a, 0)
+        self.assertEqual(match.b, 99)
+        self.assertEqual(match.size, 5)
+        self.assertEqual(a[match.a: match.a + match.size],
+                         b[match.b: match.b + match.size])
+        self.assertFalse(self.longer_match_exists(a, b, match.size))
+
+
 def test_main():
     difflib.HtmlDiff._default_prefix = 0
     Doctests = doctest.DocTestSuite(difflib)
     run_unittest(
         TestWithAscii, TestAutojunk, TestSFpatches, TestSFbugs,
-        TestOutputFormat, TestBytes, TestJunkAPIs, Doctests)
+        TestOutputFormat, TestBytes, TestJunkAPIs, TestFindLongest, Doctests)
 
 if __name__ == '__main__':
     test_main()