Class cannot subclass 'QObject' (has type 'Any') using mypy

Question

I have a class that subclasses QObject. Everyting works fine but when I run mypy on it I get the error:

"error: Class cannot subclass 'QObject' (has type 'Any')" 

At the moment I am totally stuck. I Have been reading the mypy docs but couldn't find where the error was.

Here the code:

from PyQt5.QtCore import QObject

class ServiceLocator(QObject):

    def __init__(self) -> None:
        super().__init__()
        ...

Cheers.

Triode

Have a look at this issue that appears to be the same as yours: github.com/python/mypy/issues/4180 and is related to accessing modules in other files. Guido says, "You need to tell mypy to check both files." – Patristic

This helped me. Did not solved my problem but made me achieve a "solution" – Triode

Answer 1

This error occurs when mypy doesn't have type information for a class (in your case due to a lack of stubs) and you have --disallow-subclassing-any turned on. You can either disable this flag, add typing information, or, as you pointed out, put a # type: ignore to silence the error.

Wadsworth

I recommend to use more specific error type (# type: ignore[MYPY_ERR_TYPE], [MYPY_ERR_TYPE] would be [misc] in this case) to prevent possible ignoring of all other mypy errors. – Bonneau

Answer 2

In order to leave a record on how I get around this I will answer my own question.

As the previous comment suggests, the error arise because mypy doesn't have information about QObject. I tried to add the .pyi files to mypy in the third-party folder from here or you can try building from sources PyQt5.

Everything worked but a lot of other errors arose so I finally decided to use:

#type: ignore

on this lines and get rid of the error until type hinting is better supported for this lib.

Cheers.

Triode

"until type hinting is better supported for this lib" - if you did own the lib, how would you have fixed it? – Herrod

Answer 3

This is happening to me in a library that was fully typed. The problem was that these objects were not defined as public in the __all__ variable inside of the library (doc)

Filemon

Answer 4

I had a similar problem with mypy. Fixed by adding a py.typed to my own lib from which I was importing base class.

Sovereignty

Answer 5

Just for some extra info if you encounter this - to use a config alternative but still have the full strict checking you can do the following in your mypy config:

[mypy]
# enable all additional optional checks
strict = True
# do not validate subclassing any types (without any knowledge)
disallow_subclassing_any = False

Note the order in using config and command line options with the latter ones taking precedence. This means that using --strict on the command line will ignore your config option unless you define both within the same config. I hope this helps!

Polytypic