mypy raises error on writing msgpack to binary file

[al-zatv]

Line of code which save msgpack to binary file, cause mypy to raise typing error. How can I fix typing here? Save/load works fine, by the way.

@attr.s(auto_attribs=True)
class Phrase(DataClassMessagePackMixin):
    some_data: str
....

with open(base_data_path / "my_data", "wb") as f:
        f.write(phrase.to_msgpack())

Here, mypy raises typing error:
error: Argument 1 to "write" of "IO" has incompatible type "Union[str, bytes, bytearray]"; expected "bytes"

mypy --version

mypy 0.930

[Fatal1ty]

Hello @al-zatv

At first glance it seems like to_msgpack method in DataClassMessagePackMixin should return bytes. I will see if we can change it from Union[str, bytes, bytearray] without problems. As a workaround you can use cast:

f.write(cast(bytes, phrase.to_msgpack()))

[Fatal1ty]

Fixed in 2.10.