WIP implementation of ping in Python

ping.py

#!/usr/bin/env python3
import struct
from argparse import ArgumentParser
from socket import socket, AF_INET, SOCK_DGRAM, IPPROTO_ICMP


ICMP_ECHO_REQUEST = 8


def ip_checksum(databuf, s=0):

    def carry_around_add(a, b):
        c = a + b
        return (c & 0xffff) + (c >> 16)

    for i in range(0, len(databuf), 2):
        w = (databuf[i] << 8) + databuf[i + 1]
        s = carry_around_add(s, w)
    s = ~s & 0xffff
    return s


def ping_once(sock):

    checksum = 0
    packet = bytearray(struct.pack('!bbHHh', ICMP_ECHO_REQUEST, 0, checksum, 1, 0))
    packet += bytearray([x for x in range(ord('A'), ord('Z')+1)])

    checksum = ip_checksum(packet)
    packet[2:4] = checksum.to_bytes(2, 'big')

    sock.send(packet)
    result, sender = sock.recvfrom(1024)
    result = bytearray(result)
    checksum = ip_checksum(result[:2] + result[4:])
    if checksum - len(result) != 0:
        raise ValueError("Invalid checksum in ping reply")

    return sender[0]


def do_ping(host, count, timeout):

    with socket(AF_INET, SOCK_DGRAM, IPPROTO_ICMP) as sock:
        sock.connect((host, IPPROTO_ICMP))
        print(ping_once(sock)


def main():

    p = ArgumentParser()
    p.add_argument('host')
    p.add_argument('-c', '--count', type=int, default=-1)
    args = p.parse_args()

    do_ping(args.host, args.count, 0)


if __name__ == '__main__':
    main()