python Gtk3 - 将按钮的 label 设置为默认值 None

Question

I am trying to reset a label of a button to its initial (default) value of None , which does not work as expected. Here's the minimal example:

from gi import require_version
require_version('Gtk', '3.0')
from gi.repository import Gtk


class GUI(Gtk.Window):

    def __init__(self):
        super().__init__()
        self.connect('destroy', Gtk.main_quit)
        self.set_position(Gtk.WindowPosition.CENTER)

        self.grid = Gtk.Grid(hexpand=True, vexpand=True)
        self.add(self.grid)
        button = Gtk.Button(hexpand=True, vexpand=True)
        self.grid.attach(button, 0, 0, 1, 1)
        button.connect('clicked', self.on_button_clicked)

    def on_button_clicked(self, button: Gtk.Button) -> None:
        print(label := button.get_label(), type(label))
        button.set_label(label)


def main() -> None:

    win = GUI()
    win.show_all()
    Gtk.main()


if __name__ == '__main__':
    main()

Result:

$ python example.py 
None <class 'NoneType'>
Traceback (most recent call last):
  File "/home/neumann/example.py", line 21, in on_button_clicked
    button.set_label(label)
TypeError: Argument 1 does not allow None as a value

What's the correct way to do this?

Note: Before somebody suggests it: I do not want to set the label to an empty string, since that will change the size of the button, which is noticeable on a larger grid of buttons:

from gi import require_version
require_version('Gtk', '3.0')
from gi.repository import Gtk


class GUI(Gtk.Window):

    def __init__(self):
        super().__init__()
        self.connect('destroy', Gtk.main_quit)
        self.set_position(Gtk.WindowPosition.CENTER)

        self.grid = Gtk.Grid(hexpand=True, vexpand=True)
        self.add(self.grid)
        
        for x in range(3):
            button = Gtk.Button(hexpand=True, vexpand=True)
            button.connect('clicked', self.on_button_clicked)
            self.grid.attach(button, x, 0, 1, 1)

    def on_button_clicked(self, button: Gtk.Button) -> None:
        print(label := button.get_label(), type(label))
        button.set_label('')


def main() -> None:

    win = GUI()
    win.show_all()
    Gtk.main()


if __name__ == '__main__':
    main()

Answer 1

I'm not sure what your use case is, but you can try adding a GtkLabel child and set the string there:

from gi import require_version
require_version('Gtk', '3.0')
from gi.repository import Gtk


class GUI(Gtk.Window):

    def __init__(self):
        super().__init__()
        self.connect('destroy', Gtk.main_quit)
        self.set_position(Gtk.WindowPosition.CENTER)

        self.grid = Gtk.Grid(hexpand=True, vexpand=True)
        self.add(self.grid)

        for x in range(3):
            button = Gtk.Button(hexpand=True, vexpand=True)
            label = Gtk.Label()
            button.add(label)
            button.connect('clicked', self.on_button_clicked)
            self.grid.attach(button, x, 0, 1, 1)

    def on_button_clicked(self, button: Gtk.Button) -> None:
        label = button.get_child()
        print(text := label.get_label(), type(text))
        label.set_label('')
        # or hide it if you want
        # label.hide()


def main() -> None:

    win = GUI()
    win.show_all()
    Gtk.main()


if __name__ == '__main__':
    main()

GtkButton may be creating the internal GtkLabel child only when a label is set (which should be a valid string). And since the hexpand and vexpand for the GtkButton are set to True , they may be getting propagated to the internal GtkLabel .

If you simply want all the buttons to have same width and height, you may only need grid.set_row_homogeneous() and grid.set_column_homogeneous()