PythonBeginner · Windows, macOS, or Linux with Python 3.12+

Check IP addresses against one subnet

Classify a local list of IP addresses by subnet membership.

Before you begin

  • Python 3.12 or newer
What this script changesRuns offline and only creates its result file.

Set up your example

  1. Save the complete code as ip-membership.py in a working folder.
  2. Save the provided sample files in that same folder; run commands from that folder.

Sample files in this download:

  • urls.txt
  • sample.txt
  • data.json
  • page1.json
  • page2.json
  • robots.txt
  • ips.txt

Download the ZIP, extract it, and open a terminal inside the extracted folder. The source file is ip-membership.py.

Run the script

Run command
python "ip-membership.py" --input "ips.txt" --network "192.168.1.0/24" --output "membership.json"

If your system uses python3 instead of python, use that command for Python examples. Keep paths containing spaces in quotes. Required inputs and optional settings are described in the code and setup steps.

What to expect

Classify a local list of IP addresses by subnet membership. 192.168.1.5 matches the sample /24 and 192.168.2.5 does not.

The complete script

ip-membership.py
#!/usr/bin/env python3
'Check IP addresses against one subnet'
import argparse
import json
from pathlib import Path

def write_json(path, value):
    data = json.dumps(value, indent=2, ensure_ascii=False, allow_nan=False) + "\n"
    with Path(path).open("x", encoding="utf-8", newline="") as handle:
        handle.write(data)

import urllib.request
import urllib.error
import urllib.parse
import urllib.robotparser
import socket
import ssl
import time
import re
import ipaddress
import queue
import threading
from datetime import datetime, timezone

def url(value):
    parts=urllib.parse.urlsplit(value)
    if parts.scheme not in {"http","https"} or not parts.hostname or parts.username is not None or parts.password is not None:
        raise ValueError("Use an http(s) URL without embedded credentials.")
    return value
def request(address,timeout,method="GET",headers=None,limit=1024*1024,opener=None):
    url(address)
    if not 0<timeout<=120: raise ValueError("Timeout must be 0..120 seconds, excluding zero.")
    req=urllib.request.Request(address,method=method,headers={"User-Agent":"ScriptageLearning/1.0",**(headers or {})})
    try: response=(opener.open(req,timeout=timeout) if opener else urllib.request.urlopen(req,timeout=timeout))
    except urllib.error.HTTPError as exc: response=exc
    with response:
        data=response.read(limit+1) if limit else b""
        if len(data)>limit: raise ValueError("Response exceeds the byte limit.")
        return response.status,response.geturl(),{k.lower():v for k,v in response.headers.items()},data
def checked(address,timeout,**kwargs):
    status,final,headers,data=request(address,timeout,**kwargs)
    if not 200<=status<300: raise ValueError("HTTP status "+str(status))
    return final,headers,data
def urls(path):
    result=[line.strip() for line in Path(path).read_text(encoding="utf-8").splitlines() if line.strip()]
    if len(result)>100: raise ValueError("At most 100 URLs per run.")
    return result
def resolve(host,port,timeout):
    result=queue.Queue()
    def work():
        try: result.put((True,socket.getaddrinfo(host,port,type=socket.SOCK_STREAM)))
        except OSError as exc: result.put((False,str(exc)))
    threading.Thread(target=work,daemon=True).start()
    try: ok,value=result.get(timeout=timeout)
    except queue.Empty: raise ValueError("DNS lookup timed out.")
    if not ok: raise ValueError(value)
    return value
def connect(host,port,timeout):
    last=None
    for family,kind,proto,_,address in resolve(host,port,timeout):
        connection=socket.socket(family,kind,proto)
        connection.settimeout(timeout)
        try:
            connection.connect(address)
            return connection
        except OSError as exc:
            last=exc
            connection.close()
    raise OSError(str(last))

def main():
    parser = argparse.ArgumentParser(description='Check IP addresses against one subnet')
    parser.add_argument("--output",required=True,help="New output file")
    parser.add_argument("--timeout",type=float,default=10,help="Per-operation timeout in seconds")
    parser.add_argument("--input",required=True)
    parser.add_argument("--network",required=True)
    args = parser.parse_args()
    if not 0<args.timeout<=120: raise ValueError("Timeout must be greater than zero and at most 120.")
    network=ipaddress.ip_network(args.network,strict=True)
    result=[]
    for text in Path(args.input).read_text(encoding="utf-8").splitlines():
        if not text.strip(): continue
        try:
            address=ipaddress.ip_address(text.strip())
            result.append({"address":str(address),"in_network":address in network})
        except ValueError as exc: result.append({"input":text,"error":str(exc)})
    write_json(args.output,result)

if __name__ == "__main__":
    try:
        main()
    except (OSError, ValueError, KeyError, TypeError, ArithmeticError, IndexError, LookupError) as exc:
        raise SystemExit(str(exc))

Open source as plain text · Download source and sample files

How it works

  1. The command names every destination explicitly and refuses an existing output.
  2. IPv4 and IPv6 parsing is explicit and invalid lines become error records; no packets are sent.
  3. 192.168.1.5 matches the sample /24 and 192.168.2.5 does not.

Make it your own

--network

Choose another strict CIDR network for classification.

Adapt the processing

Edit main's record to also include is_private or is_loopback for local inventory analysis.

Change one setting at a time, run it again on sample data, and compare the output. The customization guide walks through this process.

If something goes wrong

An address is invalid.

Use bare numeric IP addresses rather than hostnames or host:port strings.

The destination already exists.

Choose a new --output path. The script deliberately refuses to replace an existing result.

Reference & next steps

These official references explain the underlying tools. The Scriptage example and guide are original instructional content. See verification notes for what has been checked and the limits of those checks.

Copies a template for your own notes. It does not send anything.