为什么代码只显示XML文件的头和尾？

Question

import dpkt
import socket
import pygeoip

gi = pygeoip.GeoIP('GeoLiteCity.dat')

def main():
    f = open('wire.pcap', 'rb')
    pcap = dpkt.pcap.Reader(f)
    kmlheader = '<?xml version="1.0" encoding="UTF-8"?> \n<kml<kbd>your text         </kbd>xmlns="http://www.opengis.net/kml/2.2">\n<Document>\n'\
                 '<Style id="transBluePoly">' \
                 '<LineStyle>' \
                 '<width>1.5</width>' \
                 '<color>501400E6</color>' \
                 '</LineStyle>' \
                 '</Style>'
    kmlfooter = '</Document>\n</kml>\n'
     kmldoc=kmlheader+plotIPs(pcap)+kmlfooter
    print(kmldoc)
f = open('file.kml', 'w')
f.write(kmldoc)
f.close()

def plotIPs(pcap):
    kmlPts = ''`your text`
    for (ts, buf) in pcap:
        try:
            eth = dpkt.ethernet.Ethernet(buf)
            ip = eth.data
            src = socket.inet_ntoa(ip.src)
            dst = socket.inet_ntoa(ip.dst)
            KML = retKML(dst, src)
            kmlPts = kmlPts + KML
        except:
            pass
    return kmlPts

def retKML(dstip, srcip):
    dst = gi.record_by_name(dstip)
    src = gi.record_by_name('x.xxx.xxx.xxx')
    try:
        dstlongitude = dst['longitude']
        dstlatitude = dst['latitude']
        srclongitude = src['longitude']
        srclatitude = src['latitude']
        kml = (
            '<Placemark>\n'
            '<name>%s</name>\n'
            '<extrude>1</extrude>\n'
            '<tessellate>1</tessellate>\n'
            '<styleUrl>#transBluePoly</styleUrl>\n'
            '<LineString>\n'
            '<coordinates>%6f,%6f\n%6f,%6f</coordinates>\n'
            '</LineString>\n'
            '</Placemark>\n'
        )%(dstip, dstlongitude, dstlatitude, srclongitude, srclatitude)
        return kml
    except:
        return ''
    
if __name__ == '__main__':
    main()

我用不同的pcap文件和Geoipdata.dat试过这个。开始的时候可以正常运行，但现在（过了4天）我再试的时候，只能得到XML的头部和尾部，而不是IP地址。