base64.encodestring() and base64.decodestring() are aliases deprecated since Python 3.1: encodebytes() and decodebytes() should be used instead.

In Python 3, "string" means Unicode, whereas these functions really work at the bytes level:

>>> base64.encodestring("text")
TypeError: expected bytes-like object, not str

>>> base64.decodestring("text")
TypeError: expected bytes-like object, not str

encodebytes() and decodebytes() names are explicit on the expected types (bytes or bytes-like).

This issue is similar to bpo-38916: "Remove array.fromstring() and array.tostring() aliases, deprecated since Python 3.2".

Attached PR removes the deprecated aliases base64.encodestring() and base64.decodestring().

The deprecation was introduced 11 years ago in bpo-3613 by this change:

commit b54d801280e3f510782e2855504710947d10f053
Author: Georg Brandl <georg@python.org>
Date:   Thu Jun 4 09:11:51 2009 +0000

    #3613: add base64.encodebytes and decodebytes as the new spelling of encodestring and decodestring; deprecate the latter.

The aliases were deprecated for 7 cycles (Python 3.1 to Python 3.8).

New changeset 210c19e3c5b86535a73487fa737752de8eb1d866 by Victor Stinner in branch 'master':
bpo-39351: Remove base64.encodestring() (GH-18022)
https://github.com/python/cpython/commit/210c19e3c5b86535a73487fa737752de8eb1d866