py: Implement __delitem__ method for classes.

py/objtype.c

@@ -309,16 +309,20 @@ STATIC bool class_store_attr(mp_obj_t self_in, qstr attr, mp_obj_t value) {
 }
 
 bool class_store_item(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
+    mp_obj_class_t *self = self_in;
+    mp_obj_t member;
+    uint meth_args;
     if (value == MP_OBJ_NULL) {
         // delete item
-        // TODO implement me!
-        return false;
+        member = mp_obj_class_lookup(self->base.type, MP_QSTR___delitem__);
+        meth_args = 2;
+    } else {
+        member = mp_obj_class_lookup(self->base.type, MP_QSTR___setitem__);
+        meth_args = 3;
     }
-    mp_obj_class_t *self = self_in;
-    mp_obj_t member = mp_obj_class_lookup(self->base.type, MP_QSTR___setitem__);
     if (member != MP_OBJ_NULL) {
         mp_obj_t args[3] = {self_in, index, value};
-        mp_call_function_n_kw(member, 3, 0, args);
+        mp_call_function_n_kw(member, meth_args, 0, args);
         return true;
     } else {
         return false;

tests/basics/class_item.py

@@ -1,4 +1,4 @@
-# test class with __getitem__ and __setitem__ methods
+# test class with __getitem__, __setitem__, __delitem__ methods
 
 class C:
     def __getitem__(self, item):
@@ -8,6 +8,10 @@ class C:
     def __setitem__(self, item, value):
         print('set', item, value)
 
+    def __delitem__(self, item):
+        print('del', item)
+
 c = C()
 print(c[1])
 c[1] = 2
+del c[3]