We can probably use a closure / nonlocal with the gtk response callback, but I'm not sure if dialog.show() blocks until the window is closed or return immediately. If it blocks then we can get the the filename out of that one too.

I agree we the webagg one looks like a big lift because I don't think we currently have a response back over the websocket. Even if we added that, it is not super clear it would be useful as the filesystems that the client (in a browser possibly on a different machine) is in general not the filesystem that the server sees. There is also a good case we should not leak anything about the client file system back to the server.

If we want to differentiate between "I did not save a file" and "I can not tell you if a file was saved" we could return a different sentinel in the "I did not save a file case". The simplest thing (from an implement ion point of view...typing this proposal would be hard) would be to add NO_FILE_SAVED = object() as a class attribute on NavigationToolbar2 and return that if no file is saved.

That is a good idea. I'll do that.

Usually the FileDialogs (from Qt, Gtk etc...) return None when no file is selected. To be consistent with this behavior, I propose returning None when no file is saved and a class attribute UNKNOWN_SAVED_STATUS = object() when the status is unknown. What do you think ?

Hello,
Sorry for the delay. I think the pull request is ready for review when someone has time to do so.

"power-cycled" to re-trigger CI.

Unfortunately, this is failing on the newly-added test.

The failure is gtk setting itself up on python313:

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
200

201
self = <matplotlib.backends.backend_gtk3.FigureManagerGTK3 object at 0x7f08a8dab770>
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canvas = <backend_gtk3agg.FigureCanvasGTK3Agg object at 0x7f08a7f86c00 (matplotlib+backends+backend_gtk3agg+FigureCanvasGTK3Agg at 0x563ca08d20f0)>
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num = 1
204

205
    def __init__(self, canvas, num):
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        self._gtk_ver = gtk_ver = Gtk.get_major_version()
207
    
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        app = _create_application()
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        self.window = Gtk.Window()
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        app.add_window(self.window)
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        super().__init__(canvas, num)
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        if gtk_ver == 3:
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>           self.window.set_wmclass("matplotlib", "Matplotlib")
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E           SystemError: <slot wrapper '__getattribute__' of 'module' objects> returned a result with an exception set
216

217
lib/matplotlib/backends/_backend_gtk.py:146: SystemError

Thanks @Zybulon and congratulations on your first contribution to Matplotlib. 🎉 We hope to hear from you again!

The failing tests were not fixed yet...

which one? I thought the gtk3 python313 issue mentioned above is unrelated - Ok, my understanding: While it is unrelated, the intoduced test exercises a new gtk3 code path, which is broken.