bpo-31672 - Add one last minor clarification for idpattern (#4483)
Add one last minor clarification for idpattern
diff --git a/Doc/library/string.rst b/Doc/library/string.rst
index 5b25428..e960678 100644
--- a/Doc/library/string.rst
+++ b/Doc/library/string.rst
@@ -755,13 +755,15 @@
* *idpattern* -- This is the regular expression describing the pattern for
non-braced placeholders. The default value is the regular expression
- ``(?-i:[_a-zA-Z][_a-zA-Z0-9]*)``. If this is given and *braceidpattern* is
+ ``(?a:[_a-zA-Z][_a-zA-Z0-9]*)``. If this is given and *braceidpattern* is
``None`` this pattern will also apply to braced placeholders.
.. note::
Since default *flags* is ``re.IGNORECASE``, pattern ``[a-z]`` can match
- with some non-ASCII characters. That's why we use local ``-i`` flag here.
+ with some non-ASCII characters. That's why we use the local ``a`` flag
+ here. Further, with the default *flags* value, including ``A-Z`` in the
+ ranges is redundant, but required for backward compatibility.
While *flags* is kept to ``re.IGNORECASE`` for backward compatibility,
you can override it to ``0`` or ``re.IGNORECASE | re.ASCII`` when
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 @@
"""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