bpo-37330: open() no longer accept 'U' in file mode (GH-16959)
open(), io.open(), codecs.open() and fileinput.FileInput no longer
accept "U" ("universal newline") in the file mode. This flag was
deprecated since Python 3.3.diff --git a/Doc/library/codecs.rst b/Doc/library/codecs.rst
index f071057..ec6a053 100644
--- a/Doc/library/codecs.rst
+++ b/Doc/library/codecs.rst
@@ -197,6 +197,9 @@
*buffering* has the same meaning as for the built-in :func:`open` function.
It defaults to -1 which means that the default buffer size will be used.
+ .. versionchanged:: 3.9
+ The ``'U'`` mode has been removed.
+
.. function:: EncodedFile(file, data_encoding, file_encoding=None, errors='strict')