gh-133306: Support \z as a synonym for \Z in regular expressions (GH-133314)

\Z was an error inherited from PCRE 0.95. It was fixed in PCRE 2.0.
In other engines, \Z means not “anchor at string end”, but
“anchor before optional newline at string end”.

\z means “anchor at string end” in most RE engines.

diff --git a/Doc/howto/regex.rst b/Doc/howto/regex.rst
index 5e2f9a9d1837fe03c5f6cb973ae23f3352e26575..e543f6d5657d7989327f1e6a3f93c8a7ca942300 100644 (file)
--- a/Doc/howto/regex.rst
+++ b/Doc/howto/regex.rst
@@ -738,9 +738,12 @@ given location, they can obviously be matched an infinite number of times.
    different: ``\A`` still matches only at the beginning of the string, but ``^``
    may match at any location inside the string that follows a newline character.
 
-``\Z``
+``\z``
    Matches only at the end of the string.
 
+``\Z``
+   The same as ``\z``.  For compatibility with old Python versions.
+
 ``\b``
    Word boundary.  This is a zero-width assertion that matches only at the
    beginning or end of a word.  A word is defined as a sequence of alphanumeric

diff --git a/Doc/library/re.rst b/Doc/library/re.rst
index a91bac53fb4e75c22bbfe788b4943f580884782f..0ee2d68bcbe006d519f99cd1cb91c474260f5da7 100644 (file)
--- a/Doc/library/re.rst
+++ b/Doc/library/re.rst
@@ -266,7 +266,7 @@ The special characters are:
      not a word boundary as outside a set, and numeric escapes
      such as ``\1`` are always octal escapes, not group references.
      Special sequences which do not match a single character such as ``\A``
-     and ``\Z`` are not allowed.
+     and ``\z`` are not allowed.
 
    .. index:: single: ^ (caret); in regular expressions
 
@@ -661,11 +661,17 @@ character ``'$'``.
    matches characters which are neither alphanumeric in the current locale
    nor the underscore.
 
-.. index:: single: \Z; in regular expressions
+.. index:: single: \z; in regular expressions
+           single: \Z; in regular expressions
 
-``\Z``
+``\z``
    Matches only at the end of the string.
 
+   .. versionadded:: next
+
+``\Z``
+   The same as ``\z``.  For compatibility with old Python versions.
+
 .. index::
    single: \a; in regular expressions
    single: \b; in regular expressions

diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
index 2f8b652d47e428668c43a6151f1bcef23a703b86..6eb12f1c6f00df0f038cd4bd3468690881988848 100644 (file)
--- a/Doc/whatsnew/3.14.rst
+++ b/Doc/whatsnew/3.14.rst
@@ -624,6 +624,11 @@ Other language changes
   ASCII :class:`bytes` and :term:`bytes-like objects <bytes-like object>`.
   (Contributed by Daniel Pope in :gh:`129349`.)
 
+* Support ``\z`` as a synonym for ``\Z`` in :mod:`regular expressions <re>`.
+  It is interpreted unambiguously in many other regular expression engines,
+  unlike ``\Z``, which has subtly different behavior.
+  (Contributed by Serhiy Storchaka in :gh:`133306`.)
+
 * ``\B`` in :mod:`regular expression <re>` now matches empty input string.
   Now it is always the opposite of ``\b``.
   (Contributed by Serhiy Storchaka in :gh:`124130`.)

diff --git a/Lib/re/__init__.py b/Lib/re/__init__.py
index 7e8abbf6ffe15526495a4241ed2153d34a1beba9..af2808a77da69152b32aafb5a5c941d076921bc4 100644 (file)
--- a/Lib/re/__init__.py
+++ b/Lib/re/__init__.py
@@ -61,7 +61,7 @@ below.  If the ordinary character is not on the list, then the
 resulting RE will match the second character.
     \number  Matches the contents of the group of the same number.
     \A       Matches only at the start of the string.
-    \Z       Matches only at the end of the string.
+    \z       Matches only at the end of the string.
     \b       Matches the empty string, but only at the start or end of a word.
     \B       Matches the empty string, but not at the start or end of a word.
     \d       Matches any decimal digit; equivalent to the set [0-9] in

diff --git a/Lib/re/_parser.py b/Lib/re/_parser.py
index 0990255b22c219b778583d4e6580736ab5866f22..35ab7ede2a75a98033c08d45b0f1a181b9232cfb 100644 (file)
--- a/Lib/re/_parser.py
+++ b/Lib/re/_parser.py
@@ -49,7 +49,8 @@ CATEGORIES = {
     r"\S": (IN, [(CATEGORY, CATEGORY_NOT_SPACE)]),
     r"\w": (IN, [(CATEGORY, CATEGORY_WORD)]),
     r"\W": (IN, [(CATEGORY, CATEGORY_NOT_WORD)]),
-    r"\Z": (AT, AT_END_STRING), # end of string
+    r"\z": (AT, AT_END_STRING), # end of string
+    r"\Z": (AT, AT_END_STRING), # end of string (obsolete)
 }
 
 FLAGS = {

diff --git a/Lib/test/re_tests.py b/Lib/test/re_tests.py
index 85b026736caac8fddc86bcbcc570182639bdce1d..e50f5d52bbdec002926ba569ef46c3b4df3394c1 100755 (executable)
--- a/Lib/test/re_tests.py
+++ b/Lib/test/re_tests.py
@@ -531,7 +531,7 @@ xyzabc
     (r'a[ ]*?\ (\d+).*', 'a   10', SUCCEED, 'found', 'a   10'),
     (r'a[ ]*?\ (\d+).*', 'a    10', SUCCEED, 'found', 'a    10'),
     # bug 127259: \Z shouldn't depend on multiline mode
-    (r'(?ms).*?x\s*\Z(.*)','xx\nx\n', SUCCEED, 'g1', ''),
+    (r'(?ms).*?x\s*\z(.*)','xx\nx\n', SUCCEED, 'g1', ''),
     # bug 128899: uppercase literals under the ignorecase flag
     (r'(?i)M+', 'MMM', SUCCEED, 'found', 'MMM'),
     (r'(?i)m+', 'MMM', SUCCEED, 'found', 'MMM'),

diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py
index cf8525ed901ad3d7d37bca6aa8739fee8e481885..f79a614907899602f2cab45940058975b6781022 100644 (file)
--- a/Lib/test/test_re.py
+++ b/Lib/test/test_re.py
@@ -619,6 +619,7 @@ class ReTests(unittest.TestCase):
         self.assertEqual(re.fullmatch(r"a.*?b", "axxb").span(), (0, 4))
         self.assertIsNone(re.fullmatch(r"a+", "ab"))
         self.assertIsNone(re.fullmatch(r"abc$", "abc\n"))
+        self.assertIsNone(re.fullmatch(r"abc\z", "abc\n"))
         self.assertIsNone(re.fullmatch(r"abc\Z", "abc\n"))
         self.assertIsNone(re.fullmatch(r"(?m)abc$", "abc\n"))
         self.assertEqual(re.fullmatch(r"ab(?=c)cd", "abcd").span(), (0, 4))
@@ -802,6 +803,8 @@ class ReTests(unittest.TestCase):
         self.assertEqual(re.search(r"\B(b.)\B",
                                    "abc bcd bc abxd", re.ASCII).group(1), "bx")
         self.assertEqual(re.search(r"^abc$", "\nabc\n", re.M).group(0), "abc")
+        self.assertEqual(re.search(r"^\Aabc\z$", "abc", re.M).group(0), "abc")
+        self.assertIsNone(re.search(r"^\Aabc\z$", "\nabc\n", re.M))
         self.assertEqual(re.search(r"^\Aabc\Z$", "abc", re.M).group(0), "abc")
         self.assertIsNone(re.search(r"^\Aabc\Z$", "\nabc\n", re.M))
         self.assertEqual(re.search(br"\b(b.)\b",
@@ -813,6 +816,8 @@ class ReTests(unittest.TestCase):
         self.assertEqual(re.search(br"\B(b.)\B",
                                    b"abc bcd bc abxd", re.LOCALE).group(1), b"bx")
         self.assertEqual(re.search(br"^abc$", b"\nabc\n", re.M).group(0), b"abc")
+        self.assertEqual(re.search(br"^\Aabc\z$", b"abc", re.M).group(0), b"abc")
+        self.assertIsNone(re.search(br"^\Aabc\z$", b"\nabc\n", re.M))
         self.assertEqual(re.search(br"^\Aabc\Z$", b"abc", re.M).group(0), b"abc")
         self.assertIsNone(re.search(br"^\Aabc\Z$", b"\nabc\n", re.M))
         self.assertEqual(re.search(r"\d\D\w\W\s\S",
@@ -836,7 +841,7 @@ class ReTests(unittest.TestCase):
         self.assertEqual(re.match(r"[\^a]+", 'a^').group(), 'a^')
         self.assertIsNone(re.match(r"[\^a]+", 'b'))
         re.purge()  # for warnings
-        for c in 'ceghijklmopqyzCEFGHIJKLMNOPQRTVXY':
+        for c in 'ceghijklmopqyCEFGHIJKLMNOPQRTVXY':
             with self.subTest(c):
                 self.assertRaises(re.PatternError, re.compile, '\\%c' % c)
         for c in 'ceghijklmopqyzABCEFGHIJKLMNOPQRTVXYZ':
@@ -2608,8 +2613,8 @@ class ReTests(unittest.TestCase):
         self.assertEqual(re.findall(r'(?>(?:ab){1,3})', 'ababc'), ['abab'])
 
     def test_bug_gh91616(self):
-        self.assertTrue(re.fullmatch(r'(?s:(?>.*?\.).*)\Z', "a.txt")) # reproducer
-        self.assertTrue(re.fullmatch(r'(?s:(?=(?P<g0>.*?\.))(?P=g0).*)\Z', "a.txt"))
+        self.assertTrue(re.fullmatch(r'(?s:(?>.*?\.).*)\z', "a.txt")) # reproducer
+        self.assertTrue(re.fullmatch(r'(?s:(?=(?P<g0>.*?\.))(?P=g0).*)\z', "a.txt"))
 
     def test_bug_gh100061(self):
         # gh-100061

diff --git a/Misc/NEWS.d/next/Library/2025-05-02-21-35-03.gh-issue-133306.-vBye5.rst b/Misc/NEWS.d/next/Library/2025-05-02-21-35-03.gh-issue-133306.-vBye5.rst
new file mode 100644 (file)
index 0000000..d0973af
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-05-02-21-35-03.gh-issue-133306.-vBye5.rst
@@ -0,0 +1 @@
+Support ``\z`` as a synonym for ``\Z`` in :mod:`regular expressions <re>`.