Add @QtCore.Slot() decorations to NavigationToolbar2QT

[bersbersbers]

PR summary

Add @QtCore.Slot() decorations to NavigationToolbar2QT to suppress "Registering dynamic slot" warnings. Closes #27214.

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• [n/a] Plotting related features are demonstrated in an example
• [n/a] New Features and API Changes are noted with a directive and release note
• [n/a] Documentation complies with general and docstring guidelines

[github-actions]

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[bersbersbers]

Unfortunately, I haven't found a workaround for https://bugreports.qt.io/browse/PYSIDE-2512 that does not use a lambda. Should I add # noqa: E731 for this one?

[anntzer]

A similar workaround would be to wrap with functools.partial, i.e. QtCore.Slot()(functools.partial(getattr(self, callback))) (which all fits in a single line).

[bersbersbers]

@anntzer thanks, that's a neat idea that works locally for me. Updated the PR.

[bersbersbers]

Woohoo, all green. That wasn't too bad, just had to add some functools.wraps as well for PyQt.

Will you require a test for the emitted warning as well, or is it enough for all existing functionality to remain working?

[tacaswell]

If this indeed portable this way, can we just decorate the methods directly? Even if we have to add a bunch of methods like

@QtCore.Slot
def foo(self):
    return super().foo()

that seems better than doing the multi-layered meta-programming here!

[bersbersbers]

Yes, can do. A considerable amount of meta-programming is still done in the loop just around the snippet, so maybe a test is needed to make sure that all functions in self.toolitems have been decorated...

[bersbersbers]

Wow, that's interesting. I tried adding

    @QtCore.Slot()
    def home(self, *args):
        return super().home(*args)

    @QtCore.Slot()
    def back(self, *args):
        return super().back(*args)

    @QtCore.Slot()
    def forward(self, *args):
        return super().forward(*args)

    @QtCore.Slot()
    def pan(self, *args):
        return super().pan(*args)

    @QtCore.Slot()
    def zoom(self, *args):
        return super().zoom(*args)

    @QtCore.Slot()
    def configure_subplots(self, *args):
        return super().configure_subplots(*args)

    @QtCore.Slot()
    def edit_parameters(self, *args):
        return super().edit_parameters(*args)

    @QtCore.Slot()
    def save_figure(self, *args):
        return super().save_figure(*args)

and this works for home, back and forward - but not for the others. Irrespective of the position inside NavigationToolbar2QT, and irrespective of the order of the functions. This is with PySide6-Essentials v6.6.0.

I put this code into https://github.com/bersbersbers/matplotlib-27214/commit/a3d97f8eb2b40a46fe2d4fc4cf60f9d631fd3cf2 if anyone wants to try it themselves.

[tacaswell]

My guess is multiple inheritance is related, but do not have a good theory as to why (other than general suspicion that MI always causes problems....).

[anntzer]

If the metaprogramming approach works then let's just stick to it.

[QuLogic]

Thanks @bersbersbers! Congratulations on your first PR to Matplotlib 🎉 We hope to hear from you again.