bpo-32308: Replace empty matches adjacent to a previous non-empty mat… · pythoncapi/cpython@fbb490f · GitHub
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bpo-32308: Replace empty matches adjacent to a previous non-empty match in re.sub(). (python#4846)
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Lines changed: 35 additions & 25 deletions

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‎Doc/howto/regex.rst‎

Lines changed: 2 additions & 2 deletions

‎Doc/library/re.rst‎

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@@ -708,12 +708,15 @@ form.
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That way, separator components are always found at the same relative
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indices within the result list.
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The pattern can match empty strings. ::
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Empty matches for the pattern split the string only when not adjacent
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to a previous empty match.
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>>> re.split(r'\b', 'Words, words, words.')
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['', 'Words', ', ', 'words', ', ', 'words', '.']
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>>> re.split(r'\W*', '...words...')
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['', '', 'w', 'o', 'r', 'd', 's', '', '']
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>>> re.split(r'(\W*)', '...words...')
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['', '...', 'w', '', 'o', '', 'r', '', 'd', '', 's', '...', '']
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['', '...', '', '', 'w', '', 'o', '', 'r', '', 'd', '', 's', '...', '', '', '']
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.. versionchanged:: 3.1
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Added the optional flags argument.
@@ -778,8 +781,8 @@ form.
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The optional argument *count* is the maximum number of pattern occurrences to be
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replaced; *count* must be a non-negative integer. If omitted or zero, all
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occurrences will be replaced. Empty matches for the pattern are replaced only
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when not adjacent to a previous match, so ``sub('x*', '-', 'abc')`` returns
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``'-a-b-c-'``.
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when not adjacent to a previous empty match, so ``sub('x*', '-', 'abxd')`` returns
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``'-a-b--d-'``.
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In string-type *repl* arguments, in addition to the character escapes and
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backreferences described above,
@@ -805,6 +808,9 @@ form.
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Unknown escapes in *repl* consisting of ``'\'`` and an ASCII letter
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now are errors.
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Empty matches for the pattern are replaced when adjacent to a previous
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non-empty match.
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.. function:: subn(pattern, repl, string, count=0, flags=0)
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‎Doc/whatsnew/3.7.rst‎

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@@ -881,8 +881,9 @@ Changes in the Python API
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* The result of splitting a string on a :mod:`regular expression <re>`
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that could match an empty string has been changed. For example
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splitting on ``r'\s*'`` will now split not only on whitespaces as it
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did previously, but also between any pair of non-whitespace
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characters. The previous behavior can be restored by changing the pattern
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did previously, but also on empty strings before all non-whitespace
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characters and just before the end of the string.
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The previous behavior can be restored by changing the pattern
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to ``r'\s+'``. A :exc:`FutureWarning` was emitted for such patterns since
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Python 3.5.
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@@ -893,7 +894,13 @@ Changes in the Python API
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positions 2--3. To match only blank lines, the pattern should be rewritten
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as ``r'(?m)^[^\S\n]*$'``.
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(Contributed by Serhiy Storchaka in :issue:`25054`.)
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:func:`re.sub()` now replaces empty matches adjacent to a previous
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non-empty match. For example ``re.sub('x*', '-', 'abxd')`` returns now
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``'-a-b--d-'`` instead of ``'-a-b--d-'`` (the first minus between 'b' and
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'd' replaces 'x', and the second minus replaces an empty string between
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'x' and 'd').
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(Contributed by Serhiy Storchaka in :issue:`25054` and :issue:`32308`.)
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* :class:`tracemalloc.Traceback` frames are now sorted from oldest to most
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recent to be more consistent with :mod:`traceback`.

‎Lib/test/test_re.py‎

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Original file line numberDiff line numberDiff line change
@@ -213,11 +213,6 @@ def test_bug_114660(self):
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self.assertEqual(re.sub(r'(\S)\s+(\S)', r'\1 \2', 'hello there'),
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'hello there')
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def test_bug_462270(self):
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# Test for empty sub() behaviour, see SF bug #462270
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self.assertEqual(re.sub('x*', '-', 'abxd'), '-a-b-d-')
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self.assertEqual(re.sub('x+', '-', 'abxd'), 'ab-d')
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def test_symbolic_groups(self):
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re.compile(r'(?P<a>x)(?P=a)(?(a)y)')
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re.compile(r'(?P<a1>x)(?P=a1)(?(a1)y)')
@@ -331,10 +326,10 @@ def test_re_split(self):
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['', 'a', '', '', 'c'])
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for sep, expected in [
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(':*', ['', 'a', 'b', 'c', '']),
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('(?::*)', ['', 'a', 'b', 'c', '']),
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('(:*)', ['', ':', 'a', ':', 'b', '::', 'c', '', '']),
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('(:)*', ['', ':', 'a', ':', 'b', ':', 'c', None, '']),
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(':*', ['', '', 'a', '', 'b', '', 'c', '']),
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('(?::*)', ['', '', 'a', '', 'b', '', 'c', '']),
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('(:*)', ['', ':', '', '', 'a', ':', '', '', 'b', '::', '', '', 'c', '', '']),
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('(:)*', ['', ':', '', None, 'a', ':', '', None, 'b', ':', '', None, 'c', None, '']),
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]:
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with self.subTest(sep=sep):
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self.assertTypedEqual(re.split(sep, ':a:b::c'), expected)
@@ -357,7 +352,7 @@ def test_qualified_re_split(self):
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self.assertEqual(re.split("(:+)", ":a:b::c", maxsplit=2),
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['', ':', 'a', ':', 'b::c'])
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self.assertEqual(re.split("(:*)", ":a:b::c", maxsplit=2),
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['', ':', 'a', ':', 'b::c'])
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['', ':', '', '', 'a:b::c'])
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def test_re_findall(self):
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self.assertEqual(re.findall(":+", "abc"), [])
@@ -1753,13 +1748,13 @@ def test_match_repr(self):
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def test_zerowidth(self):
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# Issues 852532, 1647489, 3262, 25054.
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self.assertEqual(re.split(r"\b", "a::bc"), ['', 'a', '::', 'bc', ''])
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self.assertEqual(re.split(r"\b|:+", "a::bc"), ['', 'a', '', 'bc', ''])
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self.assertEqual(re.split(r"(?<!\w)(?=\w)|:+", "a::bc"), ['', 'a', 'bc'])
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self.assertEqual(re.split(r"\b|:+", "a::bc"), ['', 'a', '', '', 'bc', ''])
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self.assertEqual(re.split(r"(?<!\w)(?=\w)|:+", "a::bc"), ['', 'a', '', 'bc'])
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self.assertEqual(re.split(r"(?<=\w)(?!\w)|:+", "a::bc"), ['a', '', 'bc', ''])
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self.assertEqual(re.sub(r"\b", "-", "a::bc"), '-a-::-bc-')
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self.assertEqual(re.sub(r"\b|:+", "-", "a::bc"), '-a--bc-')
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self.assertEqual(re.sub(r"(\b|:+)", r"[\1]", "a::bc"), '[]a[][::]bc[]')
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self.assertEqual(re.sub(r"\b|:+", "-", "a::bc"), '-a---bc-')
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self.assertEqual(re.sub(r"(\b|:+)", r"[\1]", "a::bc"), '[]a[][::][]bc[]')
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self.assertEqual(re.findall(r"\b|:+", "a::bc"), ['', '', '::', '', ''])
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self.assertEqual(re.findall(r"\b|\w+", "a::bc"),

‎Misc/NEWS.d/next/Library/2017-12-13-20-31-30.bpo-32308.CUbsb2.rst‎

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@@ -0,0 +1,2 @@
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:func:`re.sub()` now replaces empty matches adjacent to a previous non-empty
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match.

‎Modules/_sre.c‎

Lines changed: 2 additions & 2 deletions

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