PyQt: Mixin that inherits from typing.Protocol : metaclass conflict: must be a subclass of the metaclasses of all its bases

hakonhagland

I am using PyQt and mypy for type checking. When I create a mixin class for a QWidget or a QMainWindow I use typing.Protocol to satisfy mypy, but then I get a run time error instead:

$ ./main.py 
Traceback (most recent call last):
  File "/home/hakon/test/python/pyqt/./main.py", line 8, in <module>
    from window import Window
  File "/home/hakon/test/python/pyqt/window.py", line 7, in <module>
    class Window(QMainWindow, ResizeWindowMixin):
TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

main.py:

#! /usr/bin/env python3

import logging
import sys

from PyQt6.QtWidgets import QApplication

from window import Window

def main() -> None:
    logging.basicConfig(level=logging.INFO)
    app = QApplication(sys.argv)
    config = {'X': '100', 'Y': '100', 'Width': '500', 'Height': '500'}
    window = Window(config)
    window.show()
    app.exec()

if __name__ == "__main__":
    main()

window.py:

from mixin import ResizeWindowMixin

from PyQt6.QtWidgets import QLabel, QVBoxLayout, QMainWindow

class Window(QMainWindow, ResizeWindowMixin):
    def __init__(self, config: dict[str, str]) -> None:
        super().__init__()
        self.window_config = config
        self.fontsize = self.window_config["FontSize"]
        self.setWindowTitle("Test Window")
        layout = QVBoxLayout()
        layout.addWidget(QLabel("Hello world!"))
        self.setLayout(layout)
        self.resize_window_from_config()

mixin.py:

from typing import Protocol

# from PyQt6.QtCore import QMetaObject

class ConfigWindow(Protocol):
    window_config: dict[str, str]

    def move(self, x: int, y: int) -> None:
        ...

    def resize(self, w: int, h: int) -> None:
        ...


class ResizeWindowMixin(ConfigWindow):
    def resize_window_from_config(self: ConfigWindow) -> None:
        if ("X" in self.window_config) and ("Y" in self.window_config):
            self.move(
                int(self.window_config["X"]),
                int(self.window_config["Y"]),
            )
        self.resize(int(self.window_config["Width"]), int(self.window_config["Height"]))

How to resolve this issue?
Note: also posted on stackoverflow: https://stackoverflow.com/q/77543597/2173773

JonB

@hakonhagland
For PyQt you will surely get answer from the PyQt mailing list if you do not elsewhere.