Slight nitpick: `bytes` objects in Python 3 do not share all of the operations and methods available on `str`, but do share quite a few. Notably, `bytes` will never implement format(), but it does implement printf()-style formatting via the modulo operator.

The `bytes` and `bytearray` types implement the following methods which also exist on `str` (in some cases, with the caveat that the operation only makes sense if the bytes in question are in the ASCII range):

capitalize(), center(), count(), endswith(), expandtabs(), find(), index(), isalnum(), isalpha(), isdigit(), islower(), isspace(), istitle(), isupper(), join(), ljust(), lower(), lstrip(), maketrans(), partition(), replace(), rfind(), rindex(), rjust(), rpartition(), rsplit(), rstrip(), split(), splitlines(), startswith(), strip(), swapcase(), title(), translate(), upper(), zfill()

If I pass a library a string it receives a Unicode string, bytes already decoded using an encoding. It shouldn't be able to re-decode that in any way, whatever that is supposed to mean on a technical level.

If a library receives a byte-array representing text, that is a completely different matter and talking about encodings is fully appropriate, even required.

But this matter should predominantly exist at your application's barrier, when doing IO.

If you're regularly doing encoding and decoding anywhere else, you're doing something wrong (or your language is).

Or do anything else that implies encoding. Like measure length, index, slice, change case etc.