I propose to add new input_type and output_type to CodecInfo. These attributes would only be defined for base64, hex, ... codecs which are not the classic encode: str=>bytes, decode: bytes=>str codecs.

I also propose to modify str.encode() and bytes.encode() to only accept codecs using the right types. If the type doesn't match, the codec raises a LookupError.

This issue should avoid the denial of service attack when a compression codec is used, see:
https://mail.python.org/pipermail/python-dev/2013-November/130188.html