How to create a Python function which accepts a list as an argument variable?

[synapticonashaikh]

Hi All,
I'm developing a module wherein I want to add some functions which take the list as an argument variable, and later on, I can process it. Please check the pseudo-code for more clarification.

#script example!
import COE
List_Variable = [6002, 0x023, "Some Random Data", 23.23]
COE.MyFunction(List_Variable)

Now, I need help with the syntactical flow and how to process this list in my function.

STATIC mp_obj_t COE_MyFunction(mp_obj_t a) 
{ 
   list_object = mp_obj_new_list (a);
   int first = MP_OBJ_SMALL_INT_VALUE(list_object[0]) + 5; //should interpret first element as integer
   int second = MP_OBJ_SMALL_INT_VALUE(list_object[1]) + 2; //should interpret second element as integer
   int8_t *third; strcpy(third, mp_obj_str_get_str(list_object[2]) ); //should interpret third element as int8_t/ uint8_t or byte array
   float  fourth =  mp_obj_new_float(list_object[3]) * 10.4f; //should interpret fourth element as float   
   return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(COE_MyFunction_obj, COE_MyFunction);

Please let me know if anyone knows how to achieve this task. Any support, hint or suggestion is highly appreciated.

[dlech]

Something like this.

STATIC mp_obj_t COE_MyFunction(mp_obj_t arg_in)  { 
   mp_int_t first = mp_obj_get_int(mp_obj_subscr(arg_in, MP_OBJ_NEW_SMALL_INT(0), MP_OBJ_SENTINEL)) + 5; //should interpret first element as integer
   mp_int_t first = mp_obj_get_int(mp_obj_subscr(arg_in, MP_OBJ_NEW_SMALL_INT(1), MP_OBJ_SENTINEL)) + 2; //should interpret second element as integer
    // assuming data is a UTF-8 string. if it is arbitrary bytes, use buffer protocol instead
   const char *third mp_obj_str_get_str(mp_obj_subscr(arg_in, MP_OBJ_NEW_SMALL_INT(2), MP_OBJ_SENTINEL)); //should interpret third element as int8_t/ uint8_t or byte array
   mp_float_t  fourth =  mp_obj_get_float(mp_obj_subscr(arg_in, MP_OBJ_NEW_SMALL_INT(3), MP_OBJ_SENTINEL)) * MICROPY_FLOAT_CONST(10.4); //should interpret fourth element as float   
   return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(COE_MyFunction_obj, COE_MyFunction);

Another option is to unpack the list in Python and use 4 args.

COE.MyFunction(*List_Variable)

[dlech]

You can look in the MicroPython source code for examples.

[synapticonashaikh]

Hello, @dlech I'm able to parse the list which I wanted to, although, I'm not sure if it is the best and most convenient way of doing it.

STATIC mp_obj_t COEOBJ_SET_OBJ_VALUE(mp_obj_t arg_in) 
{ 
    char      buffer [50]= {'\0'};
    sprintf  (buffer, "Length of list=%d\n\r",
    mp_obj_get_int(mp_obj_len(arg_in))); mp_printf(&mp_plat_print, buffer);

    /*check if the list is of 5 elements*/
 if (mp_obj_get_int(mp_obj_len(arg_in)) == (uint8_t)5)
  {
        mp_int_t index, subindex, length, flag;      
        mp_obj_t  item, iterable = mp_getiter(arg_in, NULL); 
        
        /*parse the first element of the list*/
        item  = mp_iternext(iterable);
    if (item != MP_OBJ_STOP_ITERATION || item != MP_OBJ_NULL )
      { index = mp_obj_get_int(item);
        sprintf(buffer,"Index of packet=%x\n\r", index);    
        mp_printf(&mp_plat_print, buffer); }

        /*parse the Second element of the list*/    
        item  = mp_iternext(iterable);
    if (item != MP_OBJ_STOP_ITERATION
    ||  item != MP_OBJ_NULL )
      { subindex = mp_obj_get_int(item);
        sprintf(buffer,"SubIndex of packet=%x\n\r", subindex); mp_printf(&mp_plat_print, buffer);  }

        /*parse the third element [nested list] of the list*/           
        item  = mp_iternext(iterable);
    if (item != MP_OBJ_STOP_ITERATION
    ||  item != MP_OBJ_NULL )
      { 
        sprintf  (buffer, "Length of data list=%d\n\r",
        mp_obj_get_int(mp_obj_len(item))); mp_printf(&mp_plat_print, buffer);
        mp_int_t OBJ1 = mp_obj_get_int(mp_obj_subscr(item, MP_OBJ_NEW_SMALL_INT(0), MP_OBJ_SENTINEL));
        mp_int_t OBJ2 = mp_obj_get_int(mp_obj_subscr(item, MP_OBJ_NEW_SMALL_INT(1), MP_OBJ_SENTINEL));  
        mp_int_t OBJ3 = mp_obj_get_int(mp_obj_subscr(item, MP_OBJ_NEW_SMALL_INT(2), MP_OBJ_SENTINEL));
        mp_int_t OBJ4 = mp_obj_get_int(mp_obj_subscr(item, MP_OBJ_NEW_SMALL_INT(3), MP_OBJ_SENTINEL));        
        sprintf  (buffer,"Data [0]=%x\n\r", OBJ1); mp_printf(&mp_plat_print, buffer);
        sprintf  (buffer,"Data [1]=%x\n\r", OBJ2); mp_printf(&mp_plat_print, buffer);
        sprintf  (buffer,"Data [2]=%x\n\r", OBJ3); mp_printf(&mp_plat_print, buffer);
        sprintf  (buffer,"Data [3]=%x\n\r", OBJ4); mp_printf(&mp_plat_print, buffer);      
      }  

        /*parse the fourth element of the list*/
        item  = mp_iternext(iterable);
    if (item != MP_OBJ_STOP_ITERATION
    ||  item != MP_OBJ_NULL )
      { length = mp_obj_get_int(item);
        sprintf(buffer,"Length of packet=%x\n\r", length); mp_printf(&mp_plat_print, buffer);  }

        /*parse the fifth element of the list*/
        item  = mp_iternext(iterable);
    if (item != MP_OBJ_STOP_ITERATION
    ||  item != MP_OBJ_NULL )
      { flag = mp_obj_get_int(item);
        sprintf(buffer,"Flag of packet=%x\n\r", flag); mp_printf(&mp_plat_print, buffer);  }

  }
    return mp_const_none;
}
STATIC MP_DEFINE_CONST_FUN_OBJ_1(COEOBJ_SET_OBJ_VALUE_obj, COEOBJ_SET_OBJ_VALUE);

[dlech]

FYI, mp_printf() takes a format string and varargs so you don't need a separate sprintf.

It would probably also be useful to raise exceptions on bad input instead of returning.

[synapticonashaikh]

That was the following question I had! How can I raise an exception error on bad inputs or maybe return an error to avoid unnecessary termination of the script?

[dlech]

if (length != 5) {
    mp_raise_ValueError(MP_ERROR_TEXT("arg must have length of exactly 5"));
}

On the Python side of things, you can catch and handle the error if you need to program to continue without crashing.