Get default route on Linux in Python, without imports (sorry)

get_default_route_linux.py

def default_route(verbose=False):
    """Get default route on Linux


    ATTENTION: There is a much simpler way to do this, using a dummy UDP "connection"
               and getpeername. Use that instead, it's much more portable.

    Hacky way to get the route from an interface, i.e. 'eth0' => '192.168.1.1'
    On machines that have a default route on another interface, this function
    should be used

    This configuration is especially common on testing machines where the router
    may be on a test LAN, with the default route being a different router than
    the one being targeted
    """

    if 'linux' not in platform.lower() != 'linux':
        raise RuntimeError('interface_to_router only supports Linux OS')
    
    gateway_ip = None
    default_route_field_name = 'destination'
    gateway_field_name = 'gateway'
    if verbose is True:
        print('[verbose] determining machine default route')
    route_file = open('/proc/net/route', 'rb')
    headers = route_file.readline().strip().split()
    for index, header in enumerate(headers):
        headers[index] = header.lower()

    for route_fields in [row.strip().split() for row in route_file.readlines()]:
        labeled_route_row = dict(zip(headers, route_fields))
        destination_name = labeled_route_row.get(default_route_field_name, None)
        default_route_decimal = int(destination_name, 0x10)

        if default_route_decimal == 0:
            gateway = labeled_route_row.get(gateway_field_name, None)
            gateway_decimal = htonl(int(gateway, 0x10))
            gateway_ip = inet_ntoa(pack('!I', gateway_decimal))
            if verbose is True:
                print('[verbose] found default route {}'.format(gateway_ip))
            break
    return gateway_ip

Can't guarantee this will work forever ...