invalid-bytes-returned / E0308

Message emitted:

__bytes__ does not return bytes

Description:

Used when a __bytes__ method returns something which is not bytes

Problematic code:

class CustomBytes:
    """__bytes__ returns <type 'str'>"""

    def __bytes__(self):  # [invalid-bytes-returned]
        return "123"

Correct code:

class CustomBytes:
    """__bytes__ returns <type 'bytes'>"""

    def __bytes__(self):
        return b"some bytes"

Created by the classes checker.