Mypy not treating bytes as typing.ByteString

[willmcgugan]

According to the docs, an argument typed as bytes should also accept bytearray and memoryview, but this doesn't seem to be the case.

The following example demonstrates this:

def process(b: bytes) -> None:
    pass

process(memoryview(b"foo"))

Mypy produces the following error:

error: Argument 1 to "process" has incompatible type "memoryview"; expected "bytes"

I found #4871 which is essentially the same issue. If there hasn't been any relevant changes since April 2008, perhaps its a docs issue only?

[srittau]

In typeshed I have directed people to just use bytes instead of a union with memoryview, because of the documentation. In case we just change the documentation, we'd need to change the stubs as well.

[ilevkivskyi]

I think this should be just fixed in mypy. It should be not hard, one just needs to update TYPE_PROMOTIONS_PYTHON2 and TYPE_PROMOTIONS_PYTHON3 in mypy/semanal_classprop.py and add a test for this. Anyone wants to make a PR?