'Get an un-ACKed message by delivery_tag.
If called with an invalid delivery_tag a :exc:`KeyError` is raised.
:param delivery_tag: The delivery tag associated with the message
to be returned.
:type delivery_tag: uuid.UUID
:return: An un-ACKed message that is looked up by delivery_tag.
:rtype: qpid.messaging.Message'

def get(self, delivery_tag):

    return self._not_yet_acked[delivery_tag]
