Can't get pcap file scanner to terminate normally

[Earl Eiland]

I'm using pcapy to scan a packet capture file. I've tried a variety of
tests to end the loop at EOF, but can't seem to avoid the program
terminating with a pcapy.PcapError. I've tested for empty lists (while
Raw == [] or Passed == [] and strings (while Raw ==""] or Passed ==
"" as well as the test in the sample below.

while Raw and Passed :
if Raw_IP != Passed_IP:
Dropped.dump(Raw_hdr, Raw_data)
else:
Passed_hdr, Passed_data = Passed.next()
Raw_hdr, Raw_data = Raw.next()