如何使用scapy过滤已经存在的pcap文件？

Question

我正在尝试嗅探现有的pcap文件，对其进行过滤并将其保存到新文件中，但是在运行代码时会弹出此异常。我该如何解决？

代码：

from scapy.all import *

def write(pcap):
    for pkt in pcap:
        wrpcap('filtered.pcap', pkt, append=True)  
    else:
        pass

def load_pcap(path, filter_str):
    pcap = sniff(offline=path, filter=filter_str)
    write(pcap)


def main():
    load_pcap("file.pcap", 'icmp')

main()

例外：

Traceback (most recent call last):
  File "C:\Users\myUser\AppData\Local\Programs\Python\Python37\lib\site-packages\scapy\utils.py", line 1663, in tcpdump
    stderr=stderr,
  File "C:\Users\myUser\AppData\Local\Programs\Python\Python37\lib\subprocess.py", line 756, in __init__
    restore_signals, start_new_session)
  File "C:\Users\myUser\AppData\Local\Programs\Python\Python37\lib\subprocess.py", line 1100, in _execute_child
    args = list2cmdline(args)
  File "C:\Users\myUser\AppData\Local\Programs\Python\Python37\lib\subprocess.py", line 511, in list2cmdline
    needquote = (" " in arg) or ("\t" in arg) or not arg
TypeError: argument of type 'NoneType' is not iterable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "sharkscript.py", line 140, in <module>
    main()
  File "sharkscript.py", line 137, in main
    funcs()
  File "sharkscript.py", line 130, in funcs
    options()
  File "sharkscript.py", line 95, in options
    load_pcap(get_filter(), path)
  File "sharkscript.py", line 33, in load_pcap
    pcap = sniff(offline=path, filter=filter_str)
  File "C:\Users\myUser\AppData\Local\Programs\Python\Python37\lib\site-packages\scapy\sendrecv.py", line 972, in sniff
    sniffer._run(*args, **kwargs)
  File "C:\Users\myUser\AppData\Local\Programs\Python\Python37\lib\site-packages\scapy\sendrecv.py", line 824, in _run
    )] = offline
  File "C:\Users\myUser\AppData\Local\Programs\Python\Python37\lib\site-packages\scapy\utils.py", line 1663, in tcpdump
    stderr=stderr,
  File "C:\Users\myUser\AppData\Local\Programs\Python\Python37\lib\site-packages\scapy\utils.py", line 555, in __exit__
    raise OSError(msg)
OSError: Could not execute windump(), is it installed ?

我尝试搜索windump及其安装方法，但是找不到任何东西。还有另一种方法可以过滤“离线” pcap吗？