error: Incompatible types in assignment (expression has type "AbstractKey", variable has type "PrivateKey")

[ikeikeikeike]

Tiny fix to Incompatible types in assignment error

For example.

class AbstractKey:
    @classmethod
    def _load_pkcs1_pem(cls) -> 'AbstractKey':
        pass

    @classmethod
    def load_pkcs1(cls) -> 'AbstractKey':
        return cls()


class PrivateKey(AbstractKey):
    @classmethod
    def _load_pkcs1_pem(cls) -> 'PrivateKey':
        return cls()


class PublicKey(AbstractKey):
    @classmethod
    def _load_pkcs1_pem(cls) -> 'PublicKey':
        return cls()


def main() -> None:
    akey = PrivateKey.load_pkcs1()
    pkey: PrivateKey = akey
    print(pkey)


if __name__ == '__main__':
    main()

mypy output

$ mypy main.py
main.py:25: error: Incompatible types in assignment (expression has type "AbstractKey", variable has type "PrivateKey")
Found 1 error in 1 file (checked 1 source file)

Supposedly, the python-rsa is used often like below
and then we will encounter like above an error message main.py:25 due to PrivateKey.load_pkcs1 and rsa.sign methods have incompatible types.

def func(message: bytes, private_key_string: bytes) -> bytes:
    key = rsa.PrivateKey.load_pkcs1(private_key_string)
    return rsa.sign(message, key, "SHA-1")

Might be useful to mypy option --strict if you have never seen the same message.

[sybrenstuvel]

Thanks!