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gh-152100: Support set operations in character classes (GH-152153)
Implement set difference [A--B], intersection [A&&B] and union [A||B] in regular expression character classes (Unicode Technical Standard #18), including nested, complemented and compound set operands. Symmetric difference [A~~B] remains reserved. Also use the new syntax in the standard library (_strptime, textwrap, doctest, pkgutil). Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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‎Doc/library/re.rst‎

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@@ -279,25 +279,47 @@ The special characters are:
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``[]()[{}]`` will match a right bracket, as well as left bracket, braces,
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and parentheses.
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.. .. index:: single: --; in regular expressions
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.. .. index:: single: &&; in regular expressions
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.. .. index:: single: ~~; in regular expressions
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.. .. index:: single: ||; in regular expressions
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* Support of nested sets and set operations as in `Unicode Technical
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Standard #18`_ might be added in the future. This would change the
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syntax, so to facilitate this change a :exc:`FutureWarning` will be raised
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in ambiguous cases for the time being.
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That includes sets starting with a literal ``'['`` or containing literal
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character sequences ``'--'``, ``'&&'``, ``'~~'``, and ``'||'``. To
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avoid a warning escape them with a backslash.
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.. index::
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single: --; in regular expressions
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single: &&; in regular expressions
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single: ||; in regular expressions
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* A character set may contain a nested set written in square brackets, and
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two sets may be combined with a set operator, as in `Unicode Technical
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Standard #18`_:
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* ``[A--B]`` (*difference*) matches a character that is in *A* but not
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in *B*; for example ``[a-z--[aeiou]]`` matches an ASCII lowercase
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consonant.
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* ``[A&&B]`` (*intersection*) matches a character that is in both *A*
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and *B*; for example ``[\w&&[a-z]]`` matches an ASCII lowercase letter.
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* ``[A||B]`` (*union*) matches a character that is in *A* or in *B*; this
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is the same as listing the members of both sets in a single set, but
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allows combining nested sets.
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Operators have no precedence and are applied from left to right. To
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group, write a nested set as the operand after an operator, as in
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``[a-z--[aeiou]]``. A leading ``'^'`` complements the whole result.
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A ``'['`` begins a nested set only immediately after a set operator;
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anywhere else -- including at the start of a character set -- it is an
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ordinary character, so existing patterns keep their meaning. Escape it
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as ``'\['`` to include a literal ``'['`` right after an operator.
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.. _Unicode Technical Standard #18: https://unicode.org/reports/tr18/
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.. note::
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Symmetric difference (``A~~B``) is not yet supported; a literal ``'~~'``
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in a character set still raises a :exc:`FutureWarning`.
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.. versionchanged:: 3.7
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:exc:`FutureWarning` is raised if a character set contains constructs
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that will change semantically in the future.
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.. versionchanged:: next
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Added support for nested sets and the set operators ``--``, ``&&``
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and ``||``.
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.. index:: single: | (vertical bar); in regular expressions
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``|``

‎Doc/whatsnew/3.16.rst‎

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@@ -181,6 +181,18 @@ os
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(Contributed by Maurycy Pawłowski-Wieroński in :gh:`149464`.)
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re
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--
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* :mod:`re` now supports set operations and nested sets in character classes,
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as described in `Unicode Technical Standard #18
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<https://unicode.org/reports/tr18/>`__: set difference (``[A--B]``),
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intersection (``[A&&B]``) and union (``[A||B]``), where an operand may be a
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nested set written in square brackets. For example, ``[a-z--[aeiou]]``
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matches an ASCII lowercase consonant.
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(Contributed by Serhiy Storchaka in :gh:`152100`.)
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shlex
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-----
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‎Lib/_strptime.py‎

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@@ -238,7 +238,7 @@ def __calc_date_time(self):
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current_format = current_format.replace(tz, "%Z")
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# Transform all non-ASCII digits to digits in range U+0660 to U+0669.
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if not current_format.isascii() and self.LC_alt_digits is None:
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current_format = re_sub(r'\d(?<![0-9])',
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current_format = re_sub(r'[\d--0-9]',
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lambda m: chr(0x0660 + int(m[0])),
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current_format)
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for old, new in replacement_pairs:

‎Lib/doctest.py‎

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@@ -1768,7 +1768,7 @@ def check_output(self, want, got, optionflags):
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'', want)
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# If a line in got contains only spaces, then remove the
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# spaces.
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got = re.sub(r'(?m)^[^\S\n]+$', '', got)
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got = re.sub(r'(?m)^[\s--\n]+$', '', got)
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if got == want:
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return True
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‎Lib/pkgutil.py‎

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@@ -443,7 +443,7 @@ def resolve_name(name, *, strict=False):
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within the imported package to get to the desired object.
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"""
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global _LENIENT_PATTERN, _STRICT_PATTERN
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dotted_words = r'(?!\d)(\w+)(\.(?!\d)(\w+))*'
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dotted_words = r'([\w--\d]\w*)(\.([\w--\d]\w*))*'
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if strict:
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if _STRICT_PATTERN is None:
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_STRICT_PATTERN = re.compile(

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