py/objdict: Fix __hash__ for dict_view types.

This adds a unary_op implementation for the dict_view type that makes
the implementation of `hash()` for these types compatible with CPython.

Signed-off-by: David Lechner <david@pybricks.com>

py/objdict.c

@@ -515,6 +515,15 @@ STATIC void dict_view_print(const mp_print_t *print, mp_obj_t self_in, mp_print_
     mp_print_str(print, "])");
 }
 
+STATIC mp_obj_t dict_view_unary_op(mp_unary_op_t op, mp_obj_t o_in) {
+    mp_obj_dict_view_t *o = MP_OBJ_TO_PTR(o_in);
+    // only dict.values() supports __hash__.
+    if (op == MP_UNARY_OP_HASH && o->kind == MP_DICT_VIEW_VALUES) {
+        return MP_OBJ_NEW_SMALL_INT((mp_uint_t)o_in);
+    }
+    return MP_OBJ_NULL;
+}
+
 STATIC mp_obj_t dict_view_binary_op(mp_binary_op_t op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
     // only supported for the 'keys' kind until sets and dicts are refactored
     mp_obj_dict_view_t *o = MP_OBJ_TO_PTR(lhs_in);
@@ -532,6 +541,7 @@ STATIC MP_DEFINE_CONST_OBJ_TYPE(
     MP_QSTR_dict_view,
     MP_TYPE_FLAG_ITER_IS_GETITER,
     print, dict_view_print,
+    unary_op, dict_view_unary_op,
     binary_op, dict_view_binary_op,
     iter, dict_view_getiter
     );

tests/basics/dict_views.py

@@ -18,4 +18,22 @@ try:
 except TypeError:
     print('TypeError')
 
+# keys dict_view is not hashable
+
+try:
+    hash({}.keys())
+except TypeError:
+    print('TypeError')
+
+# values dict_view is hashable
+
+print(type(hash({}.values())))
+
+# items dict_view is not hashable
+
+try:
+    hash({}.items())
+except TypeError:
+    print('TypeError')
+
 # set operations still to come