while 1:
           Py_BEGIN_ALLOW_THREADS
           n = pcap_ex_next(self.__pcap, &hdr, &pkt)
           Py_END_ALLOW_THREADS
           self._hdr = hdr
           self._pkt = pkt
           if n == 1:
               return (hdr.ts.tv_sec + (hdr.ts.tv_usec / 1000000.0),
                       PyBuffer_FromMemory(pkt, hdr.caplen))
           elif n == -1:
               raise KeyboardInterrupt
           elif n == -2:
               raise StopIteration


the problem is with a timeout. basically it doesn't work. it waits
till a packet arrive.