def event_received(pad, event):
    print "event_received"
    return

class Swap:

    @classmethod
    def swap_element(klass, swap_bin, previous_element, next_element,
        old_element, new_element):

        previous_pad = previous_element.get_static_pad("src")

        previous_pad.set_blocked(True)
        previous_element.unlink(old_element)

        #make sure data is flushed out of element2:

        old_pad = old_element.get_static_pad("src")
        handler_id = old_pad.add_event_probe(event_received)
        old_element.send_event(gst.event_new_eos())
        old_pad.remove_event_probe(handler_id)

        previous_element.unlink(old_element)
        old_element.unlink(next_element)
        old_element.set_state(gst.STATE_NULL)
        swap_bin.remove(old_element)
        swap_bin.add(new_element)
        new_element.link(next_element)
        previous_element.link(new_element)
        new_element.set_state(gst.STATE_PLAYING)
        previous_pad.set_blocked(False)
        swap_bin.set_state(gst.STATE_PLAYING)
        return