readbuffer_encode() and charbuffer_encode() are not really encoder nor related to encodings: they are related to PyBuffer. readbuffer_encode() uses "s#" format and charbuffer_encode() uses "t#" format to parse their arguments. Both functions were introduced by the creation of the _codecs module 10 years ago (r14660).

I think that these functions should be removed. memoryview() should be used instead.

Note: charbuffer_encode() is the last function using on of the "t" format (t, t#, t*) in Python3.