Working with larger modules

Once you add more and more functionality and functions to your module, it will become unmanageably, and it might make more sense to split the module into smaller components. We are going to hack our very first module, simplefunction, and factor out the function in it.

Since we will want to refer to our functions in the module definition, we have to declare them in a header file. Let us call this file helper.h. The functions declared therein operate on micropython types, so do not forget to include py/obj.h, and possibly py/runtime.h!

#include "py/obj.h"
#include "py/runtime.h"

mp_obj_t largemodule_add_ints(mp_obj_t , mp_obj_t );
mp_obj_t largemodule_subtract_ints(mp_obj_t , mp_obj_t );

Next, in helper.c, we have to implement the functions. helper.c should also contain the declarations, i.e., header.h has to be included.

#include "helper.h"

mp_obj_t largemodule_add_ints(mp_obj_t a_obj, mp_obj_t b_obj) {
    int a = mp_obj_get_int(a_obj);
    int b = mp_obj_get_int(b_obj);
    return mp_obj_new_int(a + b);

mp_obj_t largemodule_subtract_ints(mp_obj_t a_obj, mp_obj_t b_obj) {
    int a = mp_obj_get_int(a_obj);
    int b = mp_obj_get_int(b_obj);
    return mp_obj_new_int(a - b);

Finally, in the module implementation, we include helper.h, and create the function objects with MP_DEFINE_CONST_FUN_OBJ_2, and its relatives. The rest of the code is equivalent to simplefunction.c, with the only exception of the module name.

#include "py/obj.h"
#include "py/runtime.h"
#include "helper.h"

STATIC MP_DEFINE_CONST_FUN_OBJ_2(largemodule_add_ints_obj, largemodule_add_ints);
STATIC MP_DEFINE_CONST_FUN_OBJ_2(largemodule_subtract_ints_obj, largemodule_subtract_ints);

STATIC const mp_rom_map_elem_t largemodule_module_globals_table[] = {
    { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_largemodule) },
    { MP_ROM_QSTR(MP_QSTR_add_ints), MP_ROM_PTR(&largemodule_add_ints_obj) },
    { MP_ROM_QSTR(MP_QSTR_subtract_ints), MP_ROM_PTR(&largemodule_subtract_ints_obj) },
STATIC MP_DEFINE_CONST_DICT(largemodule_module_globals, largemodule_module_globals_table);

const mp_obj_module_t largemodule_user_cmodule = {
    .base = { &mp_type_module },
    .globals = (mp_obj_dict_t*)&largemodule_module_globals,

MP_REGISTER_MODULE(MP_QSTR_largemodule, largemodule_user_cmodule, MODULE_LARGEMODULE_ENABLED);

Now, since we have multiple files in our module, we have to change the makefile accordingly, and before linking, we have to compile both helper.c, and largemodule.c, thus, we add $(USERMODULES_DIR)/helper.c, and $(USERMODULES_DIR)/largemodule.c to SRC_USERMOD.


# Add all C files to SRC_USERMOD.

!make clean

import largemodule

print(largemodule.add_ints(1, 2))
print(largemodule.subtract_ints(1, 2))