如何使用python从pcap文件中过滤字符串？

import dpkt

def filter_pcap(pcap_file, filter_str):
    with open(pcap_file, 'rb') as f:
        pcap = dpkt.pcap.Reader(f)
        for ts, buf in pcap:
            # 解析数据包
            eth = dpkt.ethernet.Ethernet(buf)
            ip = eth.data
            tcp = ip.data

            # 过滤字符串
            if filter_str in tcp.data.decode('utf-8', 'ignore'):
                print(f"Filtered packet at timestamp {ts}")

# 示例用法
pcap_file = 'example.pcap'
filter_str = 'password'
filter_pcap(pcap_file, filter_str)