human
Solve the following python programming problem given the following code:
def _unset_upnp(self) : 
    def threaded_unset_upnp() : 
        u = miniupnpc.UPnP () 
        num_devices_found = u.discover () 
        if (num_devices_found > 0) : 
            u.selectigd () 
            for (port, protocol) in self.upnp_redirects : 
                if (u.getspecificportmapping (port, protocol) is None) : 
                    log.warning ('UPnP redirect for %s %d was removed by something else.', protocol, port) 
else : 
                    u.deleteportmapping (port, protocol) 
                    log.info ('Removed UPnP redirect for %s %d.', protocol, port) 
self.upnp_redirects = [] 
d = threads.deferToThread (<MASK>) 
    d.addErrback ((lambda err : str (err))) 
    return d 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: self, d
assistant
#Here is a proper replacement for <MASK>.
def threaded_unset_upnp(