Parent class in C module

[purewack]

Hello, I am trying to write a module class for an LCD screen with stream support for os.dupterm. All works well but If I extend my c class in python as class LCDExtra(LCD), then the object received by the stream_write function in c gets the LCDExtra object pointer.

Is there an easy way to retrieve the parent class in C, as I need to access some of the attributes I have defined, mainly the character cursor for printing text.

I have tried this to determine if the class is the parent class or not but I don't know how to proceed next:

static mp_uint_t lcd_stream_write(mp_obj_t self_in, const void *buf, mp_uint_t size, int *errcode) {
    lcd_obj_t *self = (lcd_obj_t*)(self_in);

    if(!mp_obj_is_type(self_in, &lcd_type)){
        // not base class, get parent here somehow
        ...
    }

    //print using hardware specific code and use poniters
    driver_print(buf,size,self->x,self->y);
    return size;
}

Here is the test code:

base = LCD()
os.dupeterm(base)
print("hello")
# works well

class LCDExtra(LCD):
    pass

extra = LCDExtra()
os.dupterm(extra)
print("hello")
# will not work as os dupterm stream write will use LCDExtra class, and the underlying c function has no access to the base class LCD

I have tried looking online but it seems the micropython code base has changed somewhat