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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def on_gtk_theme_name_changed(self, combo):
 """Set the `gtk_theme_name' property in dconf """

        citer = combo.get_active_iter()
        if not citer:
            return
        theme_name = combo.get_model().get_value(citer, 0)
        self.settings.general.set_string('gtk-theme-name', theme_name)
        select_gtk_theme(self.settings)