py/objmodule: Add support for __dict__.

This matches class `__dict__`, and is similarly gated on
MICROPY_CPYTHON_COMPAT. Unlike class though, because modules's globals are
actually dict instances, the result is a mutable dictionary.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

py/objmodule.c

@@ -89,6 +89,10 @@ STATIC void module_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
         mp_map_elem_t *elem = mp_map_lookup(&self->globals->map, MP_OBJ_NEW_QSTR(attr), MP_MAP_LOOKUP);
         if (elem != NULL) {
             dest[0] = elem->value;
+        #if MICROPY_CPYTHON_COMPAT
+        } else if (attr == MP_QSTR___dict__) {
+            dest[0] = MP_OBJ_FROM_PTR(self->globals);
+        #endif
         #if MICROPY_MODULE_GETATTR
         } else if (attr != MP_QSTR___getattr__) {
             elem = mp_map_lookup(&self->globals->map, MP_OBJ_NEW_QSTR(MP_QSTR___getattr__), MP_MAP_LOOKUP);

tests/basics/module_dict.py

@@ -0,0 +1,13 @@
+# test __dict__ attribute of a built-in module
+# see import/module_dict.py for the equivalent test on user modules
+
+import sys
+
+if not hasattr(sys, "__dict__"):
+    print("SKIP")
+    raise SystemExit
+
+
+# dict of a built-in module (read-only)
+print(type(sys.__dict__))
+print(sys.__dict__["__name__"])

tests/import/module_dict.py

@@ -0,0 +1,17 @@
+# test __dict__ attribute of a user module
+
+import sys
+
+if not hasattr(sys, "__dict__"):
+    print("SKIP")
+    raise SystemExit
+
+
+import import1b
+
+# dict of a user module (read/write)
+print(import1b.var)
+print(import1b.__dict__["var"])
+import1b.__dict__["var"] = "hello"
+print(import1b.var)
+print(import1b.__dict__["var"])