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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.
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Lines changed: 61 additions & 4 deletions

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‎Doc/library/difflib.rst‎

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@@ -421,7 +421,7 @@ The :class:`SequenceMatcher` class has this constructor:
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is not changed.
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.. method:: find_longest_match(alo, ahi, blo, bhi)
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.. method:: find_longest_match(alo=0, ahi=None, blo=0, bhi=None)
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Find longest matching block in ``a[alo:ahi]`` and ``b[blo:bhi]``.
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@@ -458,6 +458,9 @@ The :class:`SequenceMatcher` class has this constructor:
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This method returns a :term:`named tuple` ``Match(a, b, size)``.
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.. versionchanged:: 3.9
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Added default arguments.
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.. method:: get_matching_blocks()
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‎Lib/difflib.py‎

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@@ -130,7 +130,7 @@ class SequenceMatcher:
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set_seq2(b)
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Set the second sequence to be compared.
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find_longest_match(alo, ahi, blo, bhi)
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find_longest_match(alo=0, ahi=None, blo=0, bhi=None)
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Find longest matching block in a[alo:ahi] and b[blo:bhi].
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get_matching_blocks()
@@ -334,9 +334,11 @@ def __chain_b(self):
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for elt in popular: # ditto; as fast for 1% deletion
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del b2j[elt]
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def find_longest_match(self, alo, ahi, blo, bhi):
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def find_longest_match(self, alo=0, ahi=None, blo=0, bhi=None):
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"""Find longest matching block in a[alo:ahi] and b[blo:bhi].
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By default it will find the longest match in the entirety of a and b.
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If isjunk is not defined:
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Return (i,j,k) such that a[i:i+k] is equal to b[j:j+k], where
@@ -391,6 +393,10 @@ def find_longest_match(self, alo, ahi, blo, bhi):
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# the unique 'b's and then matching the first two 'a's.
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a, b, b2j, isbjunk = self.a, self.b, self.b2j, self.bjunk.__contains__
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if ahi is None:
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ahi = len(a)
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if bhi is None:
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bhi = len(b)
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besti, bestj, bestsize = alo, blo, 0
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# find longest junk-free match
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# during an iteration of the loop, j2len[j] = length of longest

‎Lib/test/test_difflib.py‎

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

‎Misc/ACKS‎

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@@ -88,6 +88,7 @@ Dwayne Bailey
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Stig Bakken
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Aleksandr Balezin
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Greg Ball
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Lewis Ball
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Luigi Ballabio
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Thomas Ballinger
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Jeff Balogh

‎Misc/NEWS.d/next/Library/2020-04-28-18-59-48.bpo-40394.Yi5uuM.rst‎

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Added default arguments to :meth:`difflib.SequenceMatcher.find_longest_match()`.

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