'Acknowledge a message by delivery_tag.
Called asynchronously once the message has been handled and can be
forgotten by the broker.
:param delivery_tag: the delivery tag associated with the message
to be acknowledged.
:type delivery_tag: uuid.UUID'

def ack(self, delivery_tag):

    message = self._not_yet_acked.pop(delivery_tag)
    self.session.acknowledge(message=message)
