'Lookup the ip for the public key to send a message to a specific node
:param trader_id: The public key of the node to send to
:type trader_id: TraderId
:return: The ip and port tuple: (<ip>, <port>)
:rtype: tuple'

def lookup_ip(self, trader_id):

    assert isinstance(trader_id, TraderId), type(trader_id)
    return self.mid_register.get(trader_id)
