py: Support object __getattr__, __delattr__ and __setattr__ methods

[dmazzella]

Related to #2375

[stinos]

Why not just #if MICROPY_PY_ATTRS_METHODS ?

[dmazzella]

becouse i have placed it into:

#if MICROPY_CPYTHON_COMPAT
....
#endif

[stinos]

Ah didin't see that in the github diff. Still it's a bit confusing as now one might use #define MICROPY_PY_ATTRS_METHODS 1 but it won't have any effect unless MICROPY_CPYTHON_COMPAT is also defined. But maybe there's no other way. Though actually this could use some cleanup: everything is already wrapped in #if MICROPY_CPYTHON_COMPAT starting at line 44 so I don't immediately see why it needs duplication.

[stinos]

'slower' would be better wording imo, without measuring the actual impact it's hard to make absolute statements about it.

[dmazzella]

Is correct to use: mp_obj_dict_get_map(self_in)

instead of:

mp_obj_type_t *type = mp_obj_get_type(self_in);
if (type->locals_dict != NULL) {
    mp_map_t *locals_map = &type->locals_dict->map;
   ...

??

[stinos]

Doesn't seem equivalent at first sight. Does everything still work if you use #define MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG 0? That would make the mp_check_self macro have effect so mp_obj_dict_get_map will assert unless a dict is passed in.

[dpgeorge]

To enable the tests, please enable this new feature in unix/mpconfigport_coverage.h and then also add a new test file.

[dmazzella]

Rebase