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#10713: Improve documentation for \b and \B and add a few tests. Initial patch and tests by Martin Pool.
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@ -325,14 +325,19 @@ the second character. For example, ``\$`` matches the character ``'$'``.
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Matches the empty string, but only at the beginning or end of a word. A word is
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defined as a sequence of alphanumeric or underscore characters, so the end of a
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word is indicated by whitespace or a non-alphanumeric, non-underscore character.
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Note that ``\b`` is defined as the boundary between ``\w`` and ``\W``, so the
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precise set of characters deemed to be alphanumeric depends on the values of the
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``UNICODE`` and ``LOCALE`` flags. Inside a character range, ``\b`` represents
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the backspace character, for compatibility with Python's string literals.
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Note that formally, ``\b`` is defined as the boundary between a ``\w`` and
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a ``\W`` character (or vice versa), or between ``\w`` and the beginning/end
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of the string, so the precise set of characters deemed to be alphanumeric
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depends on the values of the ``UNICODE`` and ``LOCALE`` flags.
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For example, ``r'\bfoo\b'`` matches ``'foo'``, ``'foo.'``, ``'(foo)'``,
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``'bar foo baz'`` but not ``'foobar'`` or ``'foo3'``.
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Inside a character range, ``\b`` represents the backspace character, for compatibility with Python's string literals.
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``\B``
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Matches the empty string, but only when it is *not* at the beginning or end of a
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word. This is just the opposite of ``\b``, so is also subject to the settings
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word. This means that ``r'py\B'`` matches ``'python'``, ``'py3'``, ``'py2'``,
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but not ``'py'``, ``'py.'``, or ``'py!'``.
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``\B`` is just the opposite of ``\b``, so is also subject to the settings
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of ``LOCALE`` and ``UNICODE``.
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``\d``
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@ -373,6 +373,32 @@ def test_special_escapes(self):
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self.assertEqual(re.search(r"\d\D\w\W\s\S",
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"1aa! a", re.UNICODE).group(0), "1aa! a")
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def test_string_boundaries(self):
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# See http://bugs.python.org/issue10713
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self.assertEqual(re.search(r"\b(abc)\b", "abc").group(1),
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"abc")
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# There's a word boundary at the start of a string.
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self.assertTrue(re.match(r"\b", "abc"))
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# A non-empty string includes a non-boundary zero-length match.
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self.assertTrue(re.search(r"\B", "abc"))
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# There is no non-boundary match at the start of a string.
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self.assertFalse(re.match(r"\B", "abc"))
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# However, an empty string contains no word boundaries, and also no
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# non-boundaries.
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self.assertEqual(re.search(r"\B", ""), None)
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# This one is questionable and different from the perlre behaviour,
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# but describes current behavior.
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self.assertEqual(re.search(r"\b", ""), None)
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# A single word-character string has two boundaries, but no
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# non-boundary gaps.
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self.assertEqual(len(re.findall(r"\b", "a")), 2)
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self.assertEqual(len(re.findall(r"\B", "a")), 0)
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# If there are no words, there are no boundaries
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self.assertEqual(len(re.findall(r"\b", " ")), 0)
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self.assertEqual(len(re.findall(r"\b", " ")), 0)
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# Can match around the whitespace.
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self.assertEqual(len(re.findall(r"\B", " ")), 2)
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def test_bigcharset(self):
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self.assertEqual(re.match(u"([\u2222\u2223])",
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u"\u2222").group(1), u"\u2222")
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