Native inet_pton and inet_ntop implementation for Python on Windows (with ctypes).

win_inet_pton.py

# This software released into the public domain. Anyone is free to copy,
# modify, publish, use, compile, sell, or distribute this software,
# either in source code form or as a compiled binary, for any purpose,
# commercial or non-commercial, and by any means.

import socket
import ctypes

class sockaddr(ctypes.Structure):
    _fields_ = [("sa_family", ctypes.c_short),
                ("__pad1", ctypes.c_ushort),
                ("ipv4_addr", ctypes.c_byte * 4),
                ("ipv6_addr", ctypes.c_byte * 16),
                ("__pad2", ctypes.c_ulong)]

WSAStringToAddressA = ctypes.windll.ws2_32.WSAStringToAddressA
WSAAddressToStringA = ctypes.windll.ws2_32.WSAAddressToStringA

def inet_pton(address_family, ip_string):
    addr = sockaddr()
    addr.sa_family = address_family
    addr_size = ctypes.c_int(ctypes.sizeof(addr))

    if WSAStringToAddressA(ip_string, address_family, None, ctypes.byref(addr), ctypes.byref(addr_size)) != 0:
        raise socket.error(ctypes.FormatError())

    if address_family == socket.AF_INET:
        return ctypes.string_at(addr.ipv4_addr, 4)
    if address_family == socket.AF_INET6:
        return ctypes.string_at(addr.ipv6_addr, 16)

    raise socket.error('unknown address family')

def inet_ntop(address_family, packed_ip):
    addr = sockaddr()
    addr.sa_family = address_family
    addr_size = ctypes.c_int(ctypes.sizeof(addr))
    ip_string = ctypes.create_string_buffer(128)
    ip_string_size = ctypes.c_int(ctypes.sizeof(ip_string))

    if address_family == socket.AF_INET:
        if len(packed_ip) != ctypes.sizeof(addr.ipv4_addr):
            raise socket.error('packed IP wrong length for inet_ntoa')
        ctypes.memmove(addr.ipv4_addr, packed_ip, 4)
    elif address_family == socket.AF_INET6:
        if len(packed_ip) != ctypes.sizeof(addr.ipv6_addr):
            raise socket.error('packed IP wrong length for inet_ntoa')
        ctypes.memmove(addr.ipv6_addr, packed_ip, 16)
    else:
        raise socket.error('unknown address family')

    if WSAAddressToStringA(ctypes.byref(addr), addr_size, None, ip_string, ctypes.byref(ip_string_size)) != 0:
        raise socket.error(ctypes.FormatError())

    return ip_string[:ip_string_size.value - 1]

You need to replace string_at with ctypes.string_at.

line 39 should read:
ip_string_size = ctypes.c_int(ctypes.sizeof(ip_string))

return ip_string[:ip_string_size.value - 1]
Since the last parameter to WSAAddressToString includes a NULL

I've fixed the above issues, done a bit of auto-setup work, and created an installable package for this:
https://github.com/hickeroar/win_inet_pton
https://pypi.python.org/pypi/win_inet_pton

Hopefully this helps some people going forward. I was about to pull my hair out when I found this. Thanks nnemkin!