'Returns an usused IP address from a specified queue.
IPs returned will be marked as used and removed from the associated
queue.
:param queue_name: ``str`` Name of the queue from which to retrieve
an IP.
:returns: IP address
:rtype: str
:raises: ip.NoSuchQueue, ip.EmptyQueue'

def get(self, queue_name):

    if (queue_name not in self._queues.keys()):
        raise NoSuchQueue('Queue    {0}    does    not    exist'.format(queue_name))
    try:
        address = self._queues[queue_name].pop(0)
    except IndexError:
        raise EmptyQueue('Queue    {0}    is    empty'.format(queue_name))
    self._used_ips.add(address)
    return address
