Type hints for utils.Lock.acquire (and __enter__) incorrect

[clo-vis]

Lock.acquire is defined as:

def acquire(...) -> typing.IO[typing.AnyStr]:

but typing.AnyStr is a TypeVar, and "A function returning TypeVar should receive at least one argument containing the same TypeVar" (this is what mypy should have said).

See https://github.com/python/mypy/issues/16113

As a result, when I write

from portalocker import Lock

def load_binary_file(path: str) -> bytes:
    with Lock(path, mode="rb") as file:
        return file.read()  #  mypy and pyright complain

I get the errors:

mypy: Incompatible return value type (got "str", expected "bytes") pyright: Return type is unknown

[wolph]

The stalebot 🤦🏻‍♂️

On the bright side, at least it reminds me of this issue. I'm working on getting portalocker pyright strict so this should be fixed soon :)

[wolph]

I've just released a new version that's got 100% strict pyright checking so you shouldn't have any issues anymore :)

[JulianJvn]

The issue is still in the current version 3.2.0. If I run mypy on the script OP provided, I get

test.py:5: error: Incompatible return value type (got "str", expected "bytes")  [return-value]
Found 1 error in 1 file (checked 1 source file)

The reason is the same as OP explained; Lock.__enter__() and Lock.acquire() return IO[AnyStr]:

https://github.com/wolph/portalocker/blob/26aaec671b84d4272488982688bf0445eb2068fa/portalocker/utils.py#L315

https://github.com/wolph/portalocker/blob/26aaec671b84d4272488982688bf0445eb2068fa/portalocker/utils.py#L244-L249

For binary file modes, this is incorrect and should be IO[bytes] instead.

Can we please reopen this issue?