combobox-kde

from gi.repository import Gtk, Gdk

class DialogExample(Gtk.Dialog):

    def __init__(self, parent):
        Gtk.Dialog.__init__(self, "My Dialog", parent, 0,
            (Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL,
             Gtk.STOCK_OK, Gtk.ResponseType.OK))

        self.set_default_size(150, 100)
        box = self.get_content_area()
        
        css = """
              GtkComboBox {
                  -GtkComboBox-appears-as-list: 1;
              }
              """
        style_provider = Gtk.CssProvider()
        style_provider.load_from_data(css)

        Gtk.StyleContext.add_provider_for_screen(
          Gdk.Screen.get_default(), 
          style_provider,     
          Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION
          )
        
        combo1 = Gtk.ComboBoxText()
        combo1.set_entry_text_column(0)
        combo1.set_active(0)
        
        for i in ["a", "b", "c", "d"]:
               combo1.append_text(i)
               
        box.add(combo1)
        self.show_all()

class DialogWindow(Gtk.Window):

    def __init__(self):
        Gtk.Window.__init__(self, title="Dialog Example")

        self.set_border_width(6)

        button = Gtk.Button("Open dialog")
        button.connect("clicked", self.on_button_clicked)

        self.add(button)

    def on_button_clicked(self, widget):
        dialog = DialogExample(self)
        response = dialog.run()

        if response == Gtk.ResponseType.OK:
            print("The OK button was clicked")
        elif response == Gtk.ResponseType.CANCEL:
            print("The Cancel button was clicked")

        dialog.destroy()

win = DialogWindow()
win.connect("delete-event", Gtk.main_quit)
win.show_all()
Gtk.main()