title: Change Style / Font of the Label of a Gtk.Button
body: <p>Environment: Python 3.4.3, GTK+ 3</p>
  
  <p>Hey there,
  I am trying to write a Gtk-application with a Gtk.ToggleButton beeing able to change the font of his Label. Here is my example, I would like to make the Label "active", which you get, when clicking the button, to be <strong>strong</strong>. </p>
  
  <pre><code>from gi.repository import Gtk
  
  class TOGGLE_WINDOW:
  
      def delete_event(self, widget, event, data=None):
          print('delete event occurred')
          return False
  
      def destroy(self, widget, data=None):
          Gtk.main_quit()
  
      def __init__(self):
          self.window = Gtk.Window()
          self.window.set_title('Toggle Button Font Change')
          self.window.connect('delete_event', self.delete_event)
          self.window.connect('destroy', self.destroy)
  
          self.box = Gtk.HBox()
          self.box.set_size_request(400, 50)
  
          self.toggle = Gtk.ToggleButton(label = 'inactive')
          self.toggle.connect('toggled', self.on_toggled, 'toggle')
  
          self.box.pack_start(self.toggle, True, True, 0)
          self.window.add(self.box)
  
          self.window.show_all()
  
      def on_toggled(self, event, widget):
          state = self.toggle.get_active()
  
          if state == True:
              self.toggle.set_label('active')
          else:
              self.toggle.set_label('inactive')
  
      def main(self):
          Gtk.main()
  
  if __name__=='__main__':
      run = TOGGLE_WINDOW()
      run.main()
  </code></pre>
  
  <p>When I try to use an external Gtk.Label to put on the Button Python says:
  <em>TypeError: Must be string, not Label</em>.
  In this case the function looks like this:</p>
  
  <pre><code>def on_toggled(self, event, widget):
      state = self.toggle.get_active()
  
      self.label = Gtk.Label()
      self.label.set_markup('&lt;b&gt;active&lt;/b&gt;')
  
      if state == True:
        self.toggle.set_label(self.label)
      else:
        self.toggle.set_label('inactive')
  </code></pre>
  
  <p>Seems, like the Buttonlabel just accepts strings.
  I also thought about converting a text to a picture and put this on the Button, but there should be an easier way...</p>
  
  <p>Thank you for ideas!</p>