Finding local IP addresses using Python's stdlib

Question

How can I find local IP addresses (i.e. 192.168.x.x or 10.0.x.x) in Python platform independently and using only the standard library?

Answer 1

This is a variant of UnkwnTech's answer -- it provides a get_local_addr() function, which returns the primary LAN ip address of the host. I'm posting it because this adds a number of things: ipv6 support, error handling, ignoring localhost/linklocal addrs, and uses a TESTNET addr (rfc5737) to connect to.

# imports
import errno
import socket
import logging

# localhost prefixes
_local_networks = ("127.", "0:0:0:0:0:0:0:1")

# ignore these prefixes -- localhost, unspecified, and link-local
_ignored_networks = _local_networks + ("0.", "0:0:0:0:0:0:0:0", "169.254.", "fe80:")

def detect_family(addr):
    if "." in addr:
        assert ":" not in addr
        return socket.AF_INET
    elif ":" in addr:
        return socket.AF_INET6
    else:
        raise ValueError("invalid ipv4/6 address: %r" % addr)

def expand_addr(addr):
    """convert address into canonical expanded form --
    no leading zeroes in groups, and for ipv6: lowercase hex, no collapsed groups.
    """
    family = detect_family(addr)
    addr = socket.inet_ntop(family, socket.inet_pton(family, addr))
    if "::" in addr:
        count = 8-addr.count(":")
        addr = addr.replace("::", (":0" * count) + ":")
        if addr.startswith(":"):
            addr = "0" + addr
    return addr

def _get_local_addr(family, remote):
    try:
        s = socket.socket(family, socket.SOCK_DGRAM)
        try:
            s.connect((remote, 9))
            return s.getsockname()[0]
        finally:
            s.close()
    except socket.error:
        # log.info("trapped error connecting to %r via %r", remote, family, exc_info=True)
        return None

def get_local_addr(remote=None, ipv6=True):
    """get LAN address of host

    :param remote:
        return  LAN address that host would use to access that specific remote address.
        by default, returns address it would use to access the public internet.

    :param ipv6:
        by default, attempts to find an ipv6 address first.
        if set to False, only checks ipv4.

    :returns:
        primary LAN address for host, or ``None`` if couldn't be determined.
    """
    if remote:
        family = detect_family(remote)
        local = _get_local_addr(family, remote)
        if not local:
            return None
        if family == socket.AF_INET6:
            # expand zero groups so the startswith() test works.
            local = expand_addr(local)
        if local.startswith(_local_networks):
            # border case where remote addr belongs to host
            return local
    else:
        # NOTE: the two addresses used here are TESTNET addresses,
        #       which should never exist in the real world.
        if ipv6:
            local = _get_local_addr(socket.AF_INET6, "2001:db8::1234")
            # expand zero groups so the startswith() test works.
            if local:
                local = expand_addr(local)
        else:
            local = None
        if not local:
            local = _get_local_addr(socket.AF_INET, "192.0.2.123")
            if not local:
                return None
    if local.startswith(_ignored_networks):
        return None
    return local