a short piece of dependency free code to get the OS netmask

cross_platform_get_netmask.py

import ipaddress
import platform
import re
import subprocess


def get_netmask(ipv4_address):
  """Gets the computer's current netmask for a given IP.
  Returns:
    str: The computer's current netmask.
  """

  if platform.system() == "Windows":
    return get_netmask_windows(ipv4_address)
  else:
    return get_netmask_linux(ipv4_address)

def get_netmask_windows(ipv4_address):
    """Gets the computer's current netmask on Windows.

    Returns:
    str: The computer's current netmask.
    """

    proc = subprocess.Popen('ipconfig', stdout=subprocess.PIPE)
    while True:
      line = proc.stdout.readline()
      if ipv4_address.encode() in line:
          break
    mask = proc.stdout.readline().rstrip().split(b':')[-1].replace(b' ', b'').decode()
    return mask


def get_netmask_linux(ipv4_address):
    """Gets the computer's current netmask on Linux.

    Returns:
    str: The computer's current netmask.
    """

    proc_output = subprocess.check_output('ip -o addr show'.split(' '))
    for line in proc_output.splitlines():
        if ipv4_address.encode() in line:
            network = line.rstrip().split(b'inet ')[1].split(b' brd')[0].decode()
            return str(ipaddress.IPv4Network(network, strict=False).netmask)


if __name__ == '__main__':
    import socket

    hostname = socket.gethostname()
    print(hostname)
    ip_address = socket.gethostbyname(hostname)
    print(ip_address)
    netmask = get_netmask(ip_address)
    print(netmask)
    if netmask is None:
        print('IP not found')
    else:
        iface = ipaddress.ip_interface(f'{ip_address}/{netmask}')
        print(iface.network.network_address)
        for ip_addr in iface.network:
            print(ip_addr)