bpo-37751: Document codecs.lookup() change in What's New in Python 3.9 (GH-23096)

diff --git a/Doc/whatsnew/3.9.rst b/Doc/whatsnew/3.9.rst
index 602ed065858ecd26275f1463fb895cd2341b4dc1..70809ff31c7f212f6e7c4ae524c80100fd40c6b2 100644 (file)
--- a/Doc/whatsnew/3.9.rst
+++ b/Doc/whatsnew/3.9.rst
@@ -1114,6 +1114,12 @@ Changes in the Python API
   compatible classes that don't inherit from those mentioned types.
   (Contributed by Roger Aiudi in :issue:`34775`).
 
+* :func:`codecs.lookup` now normalizes the encoding name the same way as
+  :func:`encodings.normalize_encoding`, except that :func:`codecs.lookup` also
+  converts the name to lower case. For example, ``"latex+latin1"`` encoding
+  name is now normalized to ``"latex_latin1"``.
+  (Contributed by Jordon Xu in :issue:`37751`.)
+
 
 Changes in the C API
 --------------------