Get local interfaces via socket. Modified from comments in https://gist.github.com/pklaus/289646

get_local_interfaces.py

""" Python2/Python3 compatible method to get local interfaces with sockets. """

import socket
import array
import struct
import fcntl

def get_local_interfaces():
    """ Returns a dictionary of name:ip key value pairs. """

    # Max possible bytes for interface result.  Will truncate if more than 4096 characters to describe interfaces.
    MAX_BYTES = 4096

    # We're going to make a blank byte array to operate on.  This is our fill char.
    FILL_CHAR = b'\0'

    # Command defined in ioctl.h for the system operation for get iface list
    # Defined at https://code.woboq.org/qt5/include/bits/ioctls.h.html under
    # /* Socket configuration controls. */ section.
    SIOCGIFCONF = 0x8912

    # Make a dgram socket to use as our file descriptor that we'll operate on.
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

    # Make a byte array with our fill character.
    names = array.array('B', MAX_BYTES * FILL_CHAR)

    # Get the address of our names byte array for use in our struct.
    names_address, names_length = names.buffer_info()

    # Create a mutable byte buffer to store the data in
    mutable_byte_buffer = struct.pack('iL', MAX_BYTES, names_address)

    # mutate our mutable_byte_buffer with the results of get_iface_list.
    # NOTE: mutated_byte_buffer is just a reference to mutable_byte_buffer - for the sake of clarity we've defined them as
    # separate variables, however they are the same address space - that's how fcntl.ioctl() works since the mutate_flag=True
    # by default.
    mutated_byte_buffer = fcntl.ioctl(sock.fileno(), SIOCGIFCONF, mutable_byte_buffer)

    # Get our max_bytes of our mutated byte buffer that points to the names variable address space.
    max_bytes_out, names_address_out = struct.unpack('iL', mutated_byte_buffer)

    # Convert names to a bytes array - keep in mind we've mutated the names array, so now our bytes out should represent
    # the bytes results of the get iface list ioctl command.
    namestr = names.tostring()

    namestr[:max_bytes_out]

    bytes_out = namestr[:max_bytes_out]

    # Each entry is 40 bytes long.  The first 16 bytes are the name string.
    # the 20-24th bytes are IP address octet strings in byte form - one for each byte.
    # Don't know what 17-19 are, or bytes 25:40.
    ip_dict = {}
    for i in range(0, max_bytes_out, 40):
        name = namestr[ i: i+16 ].split(FILL_CHAR, 1)[0]
        name = name.decode('utf-8')
        ip_bytes   = namestr[i+20:i+24]
        full_addr = []
        for netaddr in ip_bytes:
            if isinstance(netaddr, int):
                full_addr.append(str(netaddr))
            elif isinstance(netaddr, str):
                full_addr.append(str(ord(netaddr)))
        ip_dict[name] = '.'.join(full_addr)

    return ip_dict