Match and extract if found

[DeaD_EyE]

Use a set, if the order is not required.

from io import StringIO
from ipaddress import ip_address, IPv4Address


# fake file for test
ip1_content = StringIO(
    """192.168.0.1
192.168.0.2
192.168.0.3
2001:4800:7819:104:be76:4eff:fe04:5819
192.168.0.4
192.168.0.5
192.168.0.6"""
)


ip2_content = StringIO(
    """
192.168.0.799
192.168.0.900
192.168.0.3
2001:4800:7819:104:be76:4eff:fe04:5819
192.168.0.1000
192.168.0.5
192.168.0.83"""
)


def make_ipv4_set(file_like):
    results = set()

    for line in map(str.strip, file_like):
        try:
            addr = ip_address(line)
        except ValueError:
            continue

        if isinstance(addr, IPv4Address):
            results.add(addr)
            # or if you want str
            # results.add(line)

    return results


results = make_ipv4_set(ip1_content) - make_ipv4_set(ip2_content)
print(results)

• https://docs.python.org/3/library/ipaddr...ip_address
  
• https://docs.python.org/3/library/functions.html#map
  
• https://docs.python.org/3/library/stdtyp...#str.strip
  
• https://docs.python.org/3/library/stdtyp...#types-set