RustPython · youknowone · Jan 5, 2026 · Jan 3, 2026 · Jan 3, 2026 · Jan 3, 2026
diff --git a/Lib/re/__init__.py b/Lib/re/__init__.py
@@ -117,7 +117,8 @@
     U  UNICODE     For compatibility only. Ignored for string patterns (it
                    is the default), and forbidden for bytes patterns.
 
-This module also defines an exception 'error'.
+This module also defines exception 'PatternError', aliased to 'error' for
+backward compatibility.
 
 """
 
@@ -133,7 +134,7 @@
     "findall", "finditer", "compile", "purge", "escape",
     "error", "Pattern", "Match", "A", "I", "L", "M", "S", "X", "U",
     "ASCII", "IGNORECASE", "LOCALE", "MULTILINE", "DOTALL", "VERBOSE",
-    "UNICODE", "NOFLAG", "RegexFlag",
+    "UNICODE", "NOFLAG", "RegexFlag", "PatternError"
 ]
 
 __version__ = "2.2.1"
@@ -155,7 +156,7 @@ class RegexFlag:
     _numeric_repr_ = hex
 
 # sre exception
-error = _compiler.error
+PatternError = error = _compiler.PatternError
 
 # --------------------------------------------------------------------
 # public interface

diff --git a/Lib/re/_casefix.py b/Lib/re/_casefix.py
@@ -1,4 +1,4 @@
-# Auto-generated by Tools/scripts/generate_re_casefix.py.
+# Auto-generated by Tools/build/generate_re_casefix.py.
 
 # Maps the code of lowercased character to codes of different lowercased
 # characters which have the same uppercase.

diff --git a/Lib/re/_compiler.py b/Lib/re/_compiler.py
@@ -101,8 +101,6 @@ def _compile(code, pattern, flags):
             else:
                 emit(ANY)
         elif op in REPEATING_CODES:
-            if flags & SRE_FLAG_TEMPLATE:
-                raise error("internal: unsupported template operator %r" % (op,))
             if _simple(av[2]):
                 emit(REPEATING_CODES[op][2])
                 skip = _len(code); emit(0)
@@ -152,7 +150,7 @@ def _compile(code, pattern, flags):
                 if lo > MAXCODE:
                     raise error("looks too much behind")
                 if lo != hi:
-                    raise error("look-behind requires fixed-width pattern")
+                    raise PatternError("look-behind requires fixed-width pattern")
                 emit(lo) # look behind
             _compile(code, av[1], flags)
             emit(SUCCESS)
@@ -211,7 +209,7 @@ def _compile(code, pattern, flags):
             else:
                 code[skipyes] = _len(code) - skipyes + 1
         else:
-            raise error("internal: unsupported operand type %r" % (op,))
+            raise PatternError(f"internal: unsupported operand type {op!r}")
 
 def _compile_charset(charset, flags, code):
     # compile charset subprogram
@@ -237,7 +235,7 @@ def _compile_charset(charset, flags, code):
             else:
                 emit(av)
         else:
-            raise error("internal: unsupported set operator %r" % (op,))
+            raise PatternError(f"internal: unsupported set operator {op!r}")
     emit(FAILURE)
 
 def _optimize_charset(charset, iscased=None, fixup=None, fixes=None):
@@ -250,19 +248,19 @@ def _optimize_charset(charset, iscased=None, fixup=None, fixes=None):
         while True:
             try:
                 if op is LITERAL:
-                    if fixup:
-                        lo = fixup(av)
-                        charmap[lo] = 1
-                        if fixes and lo in fixes:
-                            for k in fixes[lo]:
+                    if fixup: # IGNORECASE and not LOCALE
+                        av = fixup(av)
+                        charmap[av] = 1
+                        if fixes and av in fixes:
+                            for k in fixes[av]:
                                 charmap[k] = 1
                         if not hascased and iscased(av):
                             hascased = True
                     else:
                         charmap[av] = 1
                 elif op is RANGE:
                     r = range(av[0], av[1]+1)
-                    if fixup:
+                    if fixup: # IGNORECASE and not LOCALE
                         if fixes:
                             for i in map(fixup, r):
                                 charmap[i] = 1
@@ -289,8 +287,7 @@ def _optimize_charset(charset, iscased=None, fixup=None, fixes=None):
                 # Character set contains non-BMP character codes.
                 # For range, all BMP characters in the range are already
                 # proceeded.
-                if fixup:
-                    hascased = True
+                if fixup: # IGNORECASE and not LOCALE
                     # For now, IN_UNI_IGNORE+LITERAL and
                     # IN_UNI_IGNORE+RANGE_UNI_IGNORE work for all non-BMP
                     # characters, because two characters (at least one of
@@ -301,7 +298,13 @@ def _optimize_charset(charset, iscased=None, fixup=None, fixes=None):
                     # Also, both c.lower() and c.lower().upper() are single
                     # characters for every non-BMP character.
                     if op is RANGE:
-                        op = RANGE_UNI_IGNORE
+                        if fixes: # not ASCII
+                            op = RANGE_UNI_IGNORE
+                        hascased = True
+                    else:
+                        assert op is LITERAL
+                        if not hascased and iscased(av):
+                            hascased = True
                 tail.append((op, av))
             break
 
@@ -763,4 +766,3 @@ def compile(p, flags=0):
         p.state.groups-1,
         groupindex, tuple(indexgroup)
         )
-
diff --git a/Lib/re/_constants.py b/Lib/re/_constants.py
@@ -13,14 +13,14 @@
 
 # update when constants are added or removed
 
-MAGIC = 20221023
+MAGIC = 20230612
 
 from _sre import MAXREPEAT, MAXGROUPS
 
 # SRE standard exception (access as sre.error)
 # should this really be here?
 
-class error(Exception):
+class PatternError(Exception):
     """Exception raised for invalid regular expressions.
 
     Attributes:
@@ -53,6 +53,9 @@ def __init__(self, msg, pattern=None, pos=None):
         super().__init__(msg)
 
 
+# Backward compatibility after renaming in 3.13
+error = PatternError
+
 class _NamedIntConstant(int):
     def __new__(cls, value, name):
         self = super(_NamedIntConstant, cls).__new__(cls, value)
@@ -204,7 +207,6 @@ def _makecodes(*names):
 }
 
 # flags
-SRE_FLAG_TEMPLATE = 1 # template mode (unknown purpose, deprecated)
 SRE_FLAG_IGNORECASE = 2 # case insensitive
 SRE_FLAG_LOCALE = 4 # honour system locale
 SRE_FLAG_MULTILINE = 8 # treat target as multiline string
@@ -218,4 +220,3 @@ def _makecodes(*names):
 SRE_INFO_PREFIX = 1 # has prefix
 SRE_INFO_LITERAL = 2 # entire pattern is literal (given by prefix)
 SRE_INFO_CHARSET = 4 # pattern starts with character from given set
-RE_INFO_CHARSET = 4 # pattern starts with character from given set
diff --git a/Lib/re/_parser.py b/Lib/re/_parser.py
@@ -61,12 +61,11 @@
     "x": SRE_FLAG_VERBOSE,
     # extensions
     "a": SRE_FLAG_ASCII,
-    "t": SRE_FLAG_TEMPLATE,
     "u": SRE_FLAG_UNICODE,
 }
 
 TYPE_FLAGS = SRE_FLAG_ASCII | SRE_FLAG_LOCALE | SRE_FLAG_UNICODE
-GLOBAL_FLAGS = SRE_FLAG_DEBUG | SRE_FLAG_TEMPLATE
+GLOBAL_FLAGS = SRE_FLAG_DEBUG
 
 # Maximal value returned by SubPattern.getwidth().
 # Must be larger than MAXREPEAT, MAXCODE and sys.maxsize.
@@ -781,8 +780,10 @@ def _parse(source, state, verbose, nested, first=False):
                                            source.tell() - start)
                     if char == "=":
                         subpatternappend((ASSERT, (dir, p)))
-                    else:
+                    elif p:
                         subpatternappend((ASSERT_NOT, (dir, p)))
+                    else:
+                        subpatternappend((FAILURE, ()))
                     continue
 
                 elif char == "(":

diff --git a/Lib/sre_constants.py b/Lib/sre_constants.py
@@ -5,81 +5,3 @@
 
 from re import _constants as _
 globals().update({k: v for k, v in vars(_).items() if k[:2] != '__'})
-
-if __name__ == "__main__":
-    def dump(f, d, typ, int_t, prefix):
-        items = sorted(d)
-        f.write(f"""\
-#[derive(num_enum::TryFromPrimitive, Debug)]
-#[repr({int_t})]
-#[allow(non_camel_case_types, clippy::upper_case_acronyms)]
-pub enum {typ} {{
-""")
-        for item in items:
-            name = str(item).removeprefix(prefix)
-            val = int(item)
-            f.write(f"    {name} = {val},\n")
-        f.write("""\
-}
-""")
-    import sys
-    if len(sys.argv) > 1:
-        constants_file = sys.argv[1]
-    else:
-        import os
-        constants_file = os.path.join(os.path.dirname(__file__), "../../sre-engine/src/constants.rs")
-    with open(constants_file, "w") as f:
-        f.write("""\
-/*
- * Secret Labs' Regular Expression Engine
- *
- * regular expression matching engine
- *
- * NOTE: This file is generated by sre_constants.py.  If you need
- * to change anything in here, edit sre_constants.py and run it.
- *
- * Copyright (c) 1997-2001 by Secret Labs AB.  All rights reserved.
- *
- * See the _sre.c file for information on usage and redistribution.
- */
-
-""")
-
-        f.write("use bitflags::bitflags;\n\n");
-
-        f.write("pub const SRE_MAGIC: usize = %d;\n" % MAGIC)
-
-        dump(f, OPCODES, "SreOpcode", "u32", "")
-        dump(f, ATCODES, "SreAtCode", "u32", "AT_")
-        dump(f, CHCODES, "SreCatCode", "u32", "CATEGORY_")
-
-        def bitflags(typ, int_t, prefix, flags):
-            f.write(f"""\
-bitflags! {{
-    pub struct {typ}: {int_t} {{
-""")
-            for name in flags:
-                val = globals()[prefix + name]
-                f.write(f"        const {name} = {val};\n")
-            f.write("""\
-    }
-}
-""")
-
-        bitflags("SreFlag", "u16", "SRE_FLAG_", [
-            "TEMPLATE",
-            "IGNORECASE",
-            "LOCALE",
-            "MULTILINE",
-            "DOTALL",
-            "UNICODE",
-            "VERBOSE",
-            "DEBUG",
-            "ASCII",
-        ])
-
-        bitflags("SreInfo", "u32", "SRE_INFO_", [
-            "PREFIX", "LITERAL", "CHARSET",
-        ])
-
-    print("done")