def __init__(self, publish, subscribe, unsubscribe):
    'Initialize.'
    self._pending_messages = {}
    self._publish = publish
    self._subscribe = subscribe
    self._unsubscribe = unsubscribe
Initialize.
def __init__(self, publish, subscribe, unsubscribe):
    
    self._pending_messages = {}
    self._publish = publish
    self._subscribe = subscribe
    self._unsubscribe = unsubscribe