Feed PickleBuffers to hashlib

[crusaderky]

Python 3.8.5
mypy 0.782

h = hashlib.sha1()
pickle.dumps(obj, protocol=5, buffer_callback=h.update)

mypy output:
2: error: Argument "buffer_callback" to "dumps" has incompatible type "Callable[[Union[bytes, bytearray, memoryview]], None]"; expected "Optional[Callable[[PickleBuffer], Any]]"

Expected output:
No error

[hatal175]

I think this needs python/typing#593 for a good fix. PickleBuffer implements the buffer protocol and not much more.

[srittau]

We have _typeshed.ReadableBuffer as a stopgap measure.

[hatal175]

But ReadableBuffer doesn't contain PickleBuffer

[JelleZijlstra]

@hatal175 but we could add it in the _typeshed stub.