Signature of "method" incompatible with supertype "Class" [override]

[adam-grant-hendry]

I am using mypy==0.961 exclusively (not any other static type checker; e.g. pyright, pyre, pytyped, etc.)

I've imported qtpy with PySide6 in python==3.8.10 on Windows 10 x64-bit in VSCode 1.68.1. I have the following type annotation for QtWidgets.QTabWidget.addTab

from __future__ import annotations

@overload
def addTab(
    self,
    __arg__2: str,
) -> int:
    ...

def addTab(
    self,
    __widget: PySide6.QtWidgets.QWidget,
    __label: str,
) -> int:
    ...    

PySide6 is a binding of the C++ Qt6 library using shiboken6. C++ does not natively support keyword arguments and PySide6 has chosen to support only exporting optional arguments from Qt6 as keyword arguments.

The documentation for PySide6 seems to indicate my stubs are correct, but I could be wrong.

In my source, I have a class that subclasses QTabWidget and tries to overwrite the method:

from qtpy import QtWidgets

class MyTabWidget(QtWidgets.QTabWidget):
    def addTab(
        self,
        widget: QtWidgets.QWidget,
        icon: QtGui.QIcon | QtGui.QPixmap | None,
        label: str,
    ) -> int:
        # Implementation here

However, mypy errors that the signatures are incompatible:

I suspect the problem might be due to Issue #11004, but I'm not sure.

Can anyone tell me if I am doing something wrong or if this is a bug I should # type: ignore?

[Akuli]

The mypy error is trying to say that MyTabWidget().addTab(some_widget, "hello") doesn't work. It would pass "hello" as icon, not as label. But there's an overload in QTabWidget that says it should work.

A simple solution would be to define your addTab like this:

def addTab(
    self,
    widget: QtWidgets.QWidget,
    icon: QtGui.QIcon | QtGui.QPixmap | str | None,
    label: str = "",
) -> int:
    if isinstance(icon, str):
        label = icon
        icon = None
    ...

It doesn't error in some cases where you would want an error though, such as your_tab_widget.addTab(some_widget, "foo", "bar"), but it works. You can improve on this a bit by copy/pasting the overloads from the pyqt stubs:

@overload
def addTab(
    self,
    __widget: PySide6.QtWidgets.QWidget,
    __label: str,
) -> int:
    ...    
@overload
def addTab(
    self,
    __widget: PySide6.QtWidgets.QWidget,
    __icon: QtGui.QIcon | QtGui.QPixmap | str | None,
    __label: str,
) -> int:
    ...    

def addTab(
    self,
    widget: QtWidgets.QWidget,
    icon: QtGui.QIcon | QtGui.QPixmap | str | None,
    label: str = "",
) -> int:
    if isinstance(icon, str):
        label = icon
        icon = None
    ...

In general, overriding overloaded methods isn't pretty. Are you sure that overriding this method is a good idea? Why not use "has-a" instead of "is-a" here, and just define your own method that calls self.tab_widget.addTab(...) or something like that?

[adam-grant-hendry]

@Akuli Thank you for your help!

You can improve on this a bit by copy/pasting the overloads from the pyqt stubs

I checked

• python-qt-tools/PyQt6-stubs
• python-qt-tools/PyQt5-stubs

and didn't find the implementation you showed. Did you write this, or are you pulling from a different stubs repo?

In general, overriding overloaded methods isn't pretty. Are you sure that overriding this method is a good idea?

That's a possibility...I need the widget to be substitutable wherever QTabWidget can be, so at a minimum I might need to make it subclas from QWidget, but it might be possible...

[Akuli]

Did you write this, or are you pulling from a different stubs repo?

I wrote it based on the error message. It shows how the method is stubbed under the "Superclass:" part.

Apparently PySide6 comes with a bunch of .pyi files. To find out where they are, just import PySide6 and print(PySide6). QTabWidget is defined in QtWidgets.pyi, and you can find the same overloads there.

I need the widget to be substitutable wherever QTabWidget can be

Why is this? If you are writing a library and the class is meant to be a drop-in replacement, I get it, and the best solution is to just copy/paste the overloads. If you are writing application code, just change whatever code is using the class.

[Akuli]

If you don't like copy/pasting, you could also use my @copy_type decorator: #769 (comment)

[adam-grant-hendry]

Apparently PySide6 comes with a bunch of .pyi files.

Ya, I forgot you get the script pyside6-genpyi when you pip install PySide6:

$ pyside6-genpyi all

generates the stubs, but even those use:

@overload
def addTab(self, icon: Union[PySide6.QtGui.QIcon, PySide6.QtGui.QPixmap], text: str) -> int: ...
@overload
def addTab(self, text: str) -> int: ...

so it seems you're right and overloads are going to be a bit messy...

If you are writing a library and the class is meant to be a drop-in replacement, I get it, and the best solution is to just copy/paste the overloads.

Bingo. It's a library. I'll definitely copy/paste the overloads.

[adam-grant-hendry]

@Akuli

I discovered Please add documentation about needing to re-define inherited overload signatures #10699 after your comment that I should copy/paste the overloads. I wasn't aware of this!

I actually tried the following:

import typing

from qtpy import QtWidgets, QtGui

class MyTabWidget(QtWidgets.QTabWidget):
    @typing.overload
    def addTab(  # noqa: D102
        self,
        __widget: QtWidgets.QWidget,
        __arg__2: str,
    ) -> int:
        ...

    @typing.overload
    def addTab(  # noqa: D102
        self,
        __widget: QtWidgets.QWidget,
        __icon: QtGui.QIcon | QtGui.QPixmap | None,
        __label: str,
    ) -> int:
        ...

    def addTab(
        self,
        widget: QtWidgets.QWidget,
        icon: QtGui.QIcon | QtGui.QPixmap | str | None,
        label: str,
    ) -> int:
        # Implementation here...   

and I still get the error

Overloaded function implementation does not accept all possible arguments of signature 1 [misc]

[adam-grant-hendry]

I found the actual answer is this:

class MyTabWidget(QtWidgets.QTabWidget):
    @typing.overload
    def addTab(
        self,
        widget: QtWidgets.QWidget,
        arg__2: str,
        /,
    ) -> int:  # noqa: D102  # Overloads don't get docstrings
        ...

    @typing.overload
    def addTab(
        self,
        widget: QtWidgets.QWidget,
        icon: QtGui.QIcon | QtGui.QPixmap,
        label: str,
        /,
    ) -> int:  # noqa: D102  # Overloads don't get docstrings
        ...

    def addTab(
        self,
        widget: QtWidgets.QWidget,
        icon: QtGui.QIcon | QtGui.QPixmap | str,
        label: str = '',
        /,
    ) -> int:
    # Implementation goes here...

For details, see Overloaded function implementation does not accept all possible arguments of signature #13077