#17341: Include name in re error message about invalid group name.

Patch by Jason Michalski.

Lib/sre_parse.py

@@ -600,7 +600,7 @@ def _parse(source, state):
                         if not name:
                             raise error("missing group name")
                         if not name.isidentifier():
-                            raise error("bad character in group name")
+                            raise error("bad character in group name %r" % name)
                     elif sourcematch("="):
                         # named backreference
                         name = ""
@@ -614,7 +614,8 @@ def _parse(source, state):
                         if not name:
                             raise error("missing group name")
                         if not name.isidentifier():
-                            raise error("bad character in group name")
+                            raise error("bad character in backref group name "
+                                        "%r" % name)
                         gid = state.groupdict.get(name)
                         if gid is None:
                             raise error("unknown group name")

Lib/test/test_re.py

@@ -3,6 +3,7 @@ from test.support import verbose, run_unittest, gc_collect, bigmemtest, _2G, \
 import io
 import re
 from re import Scanner
+import sre_constants
 import sys
 import string
 import traceback
@@ -1029,6 +1030,16 @@ class ReTests(unittest.TestCase):
         self.assertRaises(OverflowError, re.compile, r".{,%d}" % MAXREPEAT)
         self.assertRaises(OverflowError, re.compile, r".{%d,}?" % MAXREPEAT)
 
+    def test_backref_group_name_in_exception(self):
+        # Issue 17341: Poor error message when compiling invalid regex
+        with self.assertRaisesRegex(sre_constants.error, '<foo>'):
+            re.compile('(?P=<foo>)')
+
+    def test_group_name_in_exception(self):
+        # Issue 17341: Poor error message when compiling invalid regex
+        with self.assertRaisesRegex(sre_constants.error, '\?foo'):
+            re.compile('(?P<?foo>)')
+
 
 def run_re_tests():
     from test.re_tests import tests, SUCCEED, FAIL, SYNTAX_ERROR

Misc/ACKS

@@ -805,6 +805,7 @@ Piotr Meyer
 Alexis Métaireau
 Steven Miale
 Trent Mick
+Jason Michalski
 Franck Michea
 Tom Middleton
 Stan Mihai

Misc/NEWS

@@ -29,6 +29,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #17341: Include the invalid name in the error messages from re about
+  invalid group names.
+
 - Issue #17702: os.environ now raises KeyError with the original environment
   variable name (str on UNIX), instead of using the encoded name (bytes on
   UNIX).