Something

def OnSolo(self, widget,event):
		"""
		Toggles soloing the instrument on/off.
		It will also update the pressed in/out look of the button.
                If CTRL is pressed, several solo instruments are allowed.
		"""
		if not self.Updating:
                    if 'GDK_CONTROL_MASK' not in event.state.value_names:
                        for instrument in self.project.instruments:
                            if instrument.isSolo and instrument is not self.instrument:
                                instrument.ToggleSolo(instrument.isMuted)
                    self.instrument.ToggleSolo(False)