'Pass a `KeyEvent` to all functions connected to ``key_release_event``.'

def key_release_event(self, key, guiEvent=None):

    s = u'key_release_event'
    event = KeyEvent(s, self, key, self._lastx, self._lasty, guiEvent=guiEvent)
    self.callbacks.process(s, event)
    self._key = None
