pyshark无法在Windows 7(python)上捕获数据包

这是我的python代码

import pyshark
def NetCap():
    print 'capturing...'
    livecapture = pyshark.LiveCapture(interface="eth0",output_file='./test.pcapng')
    livecapture.sniff(packet_count=10)
    print 'end of capture.'
    print livecapture

if __name__ == "__main__":
    NetCap()

这是结果

capturing...
end of capture.
<LiveCapture (0 packets)>

Livecapture是0包.
我不知道是怎么回事.
请帮我.