bpo-31672 - Add one last minor clarification for idpattern (#4483)

Add one last minor clarification for idpattern

1 files changed, 7 insertions, 4 deletions

diff --git a/Lib/string.py b/Lib/string.py
index a3e6d91..fd4b1f7 100644
--- a/Lib/string.py
+++ b/Lib/string.py
@@ -79,11 +79,14 @@ class Template(metaclass=_TemplateMetaclass):
     """A string class for supporting $-substitutions."""
 
     delimiter = '$'
-    # r'[a-z]' matches to non-ASCII letters when used with IGNORECASE,
-    # but without ASCII flag.  We can't add re.ASCII to flags because of
-    # backward compatibility.  So we use local -i flag and [a-zA-Z] pattern.
+    # r'[a-z]' matches to non-ASCII letters when used with IGNORECASE, but
+    # without the ASCII flag.  We can't add re.ASCII to flags because of
+    # backward compatibility.  So we use the ?a local flag and [a-z] pattern.
+    # We also can't remove the A-Z ranges, because although they are
+    # technically redundant with the IGNORECASE flag, the value is part of the
+    # publicly documented API.
     # See https://bugs.python.org/issue31672
-    idpattern = r'(?-i:[_a-zA-Z][_a-zA-Z0-9]*)'
+    idpattern = r'(?a:[_a-zA-Z][_a-zA-Z0-9]*)'
     braceidpattern = None
     flags = _re.IGNORECASE