ByteString, specifying length for any bytes-like variable

This request is a combination of two additions to ByteString that apparently are not supported yet, or at least I could find no discussion of them.

• Support any bytes-like buffers, not only bytes, bytearray and memoryview
• Allow specifying the length of the buffer expected (in my case it usually must be exactly 32 bytes)

Ideally, Python typing would allow specifying bytes-like of (a) any length, (b) fixed length or (c) min and/or max length. Potentially also separately specifying if a writable buffer is expected.

While I don't expect for mypy to be able to check for all of that, it would at least be nice to include such information in the annotations for documentation purposes, avoiding the use of docstrings for parameter definitions where names and types are descriptive enough. Is there any way to do this without causing mypy errors, considering that I would rather have no type checking but documentative annotations than what the current implementation can do?

Non vengono indicati file, test o punti di ingresso. Inizia esaminando il comportamento esistente del tipaggio di ByteString e le discussioni correlate sul tipaggio, quindi determina se i tipi simili a bytes, le lunghezze fisse o limitate e la scrivibilità possano essere rappresentati senza errori di mypy. Il lavoro sarà considerato completato quando saranno disponibili un design delle annotazioni concordato e il comportamento documentato del controllo dei tipi.