Encoding and decoding, in the most general sense, can include unicode -> unicode and bytestring -> bytestring.

I can't see any standard unicode->unicode encodings in Python 2.7

https://docs.python.org/2/library/codecs.html

but we can create one:

py> import codecs
py> class NullCodec(codecs.Codec):  # "do nothing" codec
...     def encode(self, input, errors='strict'):
...         return (input, len(input))
...     def decode(self, input, errors='strict'):
...         return (input, len(input))
...
py> def getregentry(name):
...     return codecs.CodecInfo(
...         name='null',
...         encode=NullCodec().encode,
...         decode=NullCodec().decode,
...         incrementalencoder=None,
...         incrementaldecoder=None,
...         streamwriter=None,
...         streamreader=None,
...     )
...
py> codecs.register(getregentry)
py> u'unicode text'.encode('null')
u'unicode text'


so the documentation is correct, and the Stackoverflow answer is not.