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bpo-32308: Replace empty matches adjacent to a previous non-empty match in re.sub(). (#4846)

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Serhiy Storchaka 2018-01-04 11:06:13 +02:00 committed by GitHub
parent 0cc99c8cd7
commit fbb490fd2f
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6 changed files with 35 additions and 25 deletions
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4
Doc/howto/regex.rst
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@ -1140,12 +1140,12 @@ new string value and the number of replacements that were performed::
>>> p.subn('colour', 'no colours at all')
('no colours at all', 0)
Empty matches are replaced only when they're not adjacent to a previous match.
Empty matches are replaced only when they're not adjacent to a previous empty match.
::
>>> p = re.compile('x*')
>>> p.sub('-', 'abxd')
'-a-b-d-'
'-a-b--d-'
If *replacement* is a string, any backslash escapes in it are processed. That
is, ``\n`` is converted to a single newline character, ``\r`` is converted to a

14
Doc/library/re.rst
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@ -708,12 +708,15 @@ form.
That way, separator components are always found at the same relative
indices within the result list.
The pattern can match empty strings. ::
Empty matches for the pattern split the string only when not adjacent
to a previous empty match.
>>> re.split(r'\b', 'Words, words, words.')
['', 'Words', ', ', 'words', ', ', 'words', '.']
>>> re.split(r'\W*', '...words...')
['', '', 'w', 'o', 'r', 'd', 's', '', '']
>>> re.split(r'(\W*)', '...words...')
['', '...', 'w', '', 'o', '', 'r', '', 'd', '', 's', '...', '']
['', '...', '', '', 'w', '', 'o', '', 'r', '', 'd', '', 's', '...', '', '', '']
.. versionchanged:: 3.1
Added the optional flags argument.
@ -778,8 +781,8 @@ form.
The optional argument *count* is the maximum number of pattern occurrences to be
replaced; *count* must be a non-negative integer. If omitted or zero, all
occurrences will be replaced. Empty matches for the pattern are replaced only
when not adjacent to a previous match, so ``sub('x*', '-', 'abc')`` returns
``'-a-b-c-'``.
when not adjacent to a previous empty match, so ``sub('x*', '-', 'abxd')`` returns
``'-a-b--d-'``.
In string-type *repl* arguments, in addition to the character escapes and
backreferences described above,
@ -805,6 +808,9 @@ form.
Unknown escapes in *repl* consisting of ``'\'`` and an ASCII letter
now are errors.
Empty matches for the pattern are replaced when adjacent to a previous
non-empty match.
.. function:: subn(pattern, repl, string, count=0, flags=0)

13
Doc/whatsnew/3.7.rst
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@ -881,8 +881,9 @@ Changes in the Python API
* The result of splitting a string on a :mod:`regular expression <re>`
that could match an empty string has been changed. For example
splitting on ``r'\s*'`` will now split not only on whitespaces as it
did previously, but also between any pair of non-whitespace
characters. The previous behavior can be restored by changing the pattern
did previously, but also on empty strings before all non-whitespace
characters and just before the end of the string.
The previous behavior can be restored by changing the pattern
to ``r'\s+'``. A :exc:`FutureWarning` was emitted for such patterns since
Python 3.5.
@ -893,7 +894,13 @@ Changes in the Python API
positions 2--3. To match only blank lines, the pattern should be rewritten
as ``r'(?m)^[^\S\n]*$'``.
(Contributed by Serhiy Storchaka in :issue:`25054`.)
:func:`re.sub()` now replaces empty matches adjacent to a previous
non-empty match. For example ``re.sub('x*', '-', 'abxd')`` returns now
``'-a-b--d-'`` instead of ``'-a-b--d-'`` (the first minus between 'b' and
'd' replaces 'x', and the second minus replaces an empty string between
'x' and 'd').
(Contributed by Serhiy Storchaka in :issue:`25054` and :issue:`32308`.)
* :class:`tracemalloc.Traceback` frames are now sorted from oldest to most
recent to be more consistent with :mod:`traceback`.

23
Lib/test/test_re.py
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@ -213,11 +213,6 @@ class ReTests(unittest.TestCase):
self.assertEqual(re.sub(r'(\S)\s+(\S)', r'\1 \2', 'hello there'),
'hello there')
def test_bug_462270(self):
# Test for empty sub() behaviour, see SF bug #462270
self.assertEqual(re.sub('x*', '-', 'abxd'), '-a-b-d-')
self.assertEqual(re.sub('x+', '-', 'abxd'), 'ab-d')
def test_symbolic_groups(self):
re.compile(r'(?P<a>x)(?P=a)(?(a)y)')
re.compile(r'(?P<a1>x)(?P=a1)(?(a1)y)')
@ -331,10 +326,10 @@ class ReTests(unittest.TestCase):
['', 'a', '', '', 'c'])
for sep, expected in [
(':*', ['', 'a', 'b', 'c', '']),
('(?::*)', ['', 'a', 'b', 'c', '']),
('(:*)', ['', ':', 'a', ':', 'b', '::', 'c', '', '']),
('(:)*', ['', ':', 'a', ':', 'b', ':', 'c', None, '']),
(':*', ['', '', 'a', '', 'b', '', 'c', '']),
('(?::*)', ['', '', 'a', '', 'b', '', 'c', '']),
('(:*)', ['', ':', '', '', 'a', ':', '', '', 'b', '::', '', '', 'c', '', '']),
('(:)*', ['', ':', '', None, 'a', ':', '', None, 'b', ':', '', None, 'c', None, '']),
]:
with self.subTest(sep=sep):
self.assertTypedEqual(re.split(sep, ':a:b::c'), expected)
@ -357,7 +352,7 @@ class ReTests(unittest.TestCase):
self.assertEqual(re.split("(:+)", ":a:b::c", maxsplit=2),
['', ':', 'a', ':', 'b::c'])
self.assertEqual(re.split("(:*)", ":a:b::c", maxsplit=2),
['', ':', 'a', ':', 'b::c'])
['', ':', '', '', 'a:b::c'])
def test_re_findall(self):
self.assertEqual(re.findall(":+", "abc"), [])
@ -1753,13 +1748,13 @@ class ReTests(unittest.TestCase):
def test_zerowidth(self):
# Issues 852532, 1647489, 3262, 25054.
self.assertEqual(re.split(r"\b", "a::bc"), ['', 'a', '::', 'bc', ''])
self.assertEqual(re.split(r"\b|:+", "a::bc"), ['', 'a', '', 'bc', ''])
self.assertEqual(re.split(r"(?<!\w)(?=\w)|:+", "a::bc"), ['', 'a', 'bc'])
self.assertEqual(re.split(r"\b|:+", "a::bc"), ['', 'a', '', '', 'bc', ''])
self.assertEqual(re.split(r"(?<!\w)(?=\w)|:+", "a::bc"), ['', 'a', '', 'bc'])
self.assertEqual(re.split(r"(?<=\w)(?!\w)|:+", "a::bc"), ['a', '', 'bc', ''])
self.assertEqual(re.sub(r"\b", "-", "a::bc"), '-a-::-bc-')
self.assertEqual(re.sub(r"\b|:+", "-", "a::bc"), '-a--bc-')
self.assertEqual(re.sub(r"(\b|:+)", r"[\1]", "a::bc"), '[]a[][::]bc[]')
self.assertEqual(re.sub(r"\b|:+", "-", "a::bc"), '-a---bc-')
self.assertEqual(re.sub(r"(\b|:+)", r"[\1]", "a::bc"), '[]a[][::][]bc[]')
self.assertEqual(re.findall(r"\b|:+", "a::bc"), ['', '', '::', '', ''])
self.assertEqual(re.findall(r"\b|\w+", "a::bc"),

2
Misc/NEWS.d/next/Library/2017-12-13-20-31-30.bpo-32308.CUbsb2.rst Normal file
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@ -0,0 +1,2 @@
:func:`re.sub()` now replaces empty matches adjacent to a previous non-empty
match.

4
Modules/_sre.c
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@ -955,7 +955,7 @@ _sre_SRE_Pattern_split_impl(PatternObject *self, PyObject *string,
}
n = n + 1;
state.must_advance = 1;
state.must_advance = (state.ptr == state.start);
last = state.start = state.ptr;
}
@ -1109,7 +1109,7 @@ pattern_subx(PatternObject* self, PyObject* ptemplate, PyObject* string,
i = e;
n = n + 1;
state.must_advance = 1;
state.must_advance = (state.ptr == state.start);
state.start = state.ptr;
}