Add empty (false) value testing for strings, tuples, lists, dicts.

py/runtime.c

@@ -297,6 +297,24 @@ int rt_is_true(mp_obj_t arg) {
         return 0;
     } else if (arg == mp_const_true) {
         return 1;
+    } else if (MP_OBJ_IS_QSTR(arg)) {
+        // TODO: \0
+        return *qstr_str(MP_OBJ_QSTR_VALUE(arg)) != 0;
+    } else if (MP_OBJ_IS_TYPE(arg, &str_type)) {
+        // TODO: \0
+        return *qstr_str(mp_obj_str_get(arg)) != 0;
+    } else if (MP_OBJ_IS_TYPE(arg, &list_type)) {
+        uint len;
+        mp_obj_t *dummy;
+        mp_obj_list_get(arg, &len, &dummy);
+        return len != 0;
+    } else if (MP_OBJ_IS_TYPE(arg, &tuple_type)) {
+        uint len;
+        mp_obj_t *dummy;
+        mp_obj_tuple_get(arg, &len, &dummy);
+        return len != 0;
+    } else if (MP_OBJ_IS_TYPE(arg, &dict_type)) {
+        return mp_obj_dict_len(arg) != 0;
     } else {
         assert(0);
         return 0;

tests/basics/tests/true-value.py

@@ -0,0 +1,27 @@
+# Test true-ish value handling
+
+if not False:
+    print("False")
+
+if not 0:
+    print("0")
+
+if not "":
+    print("Empty string")
+if "foo":
+    print("Non-empty string")
+
+if not ():
+    print("Empty tuple")
+if ("",):
+    print("Non-empty tuple")
+
+if not []:
+    print("Empty list")
+if [0]:
+    print("Non-empty list")
+
+if not {}:
+    print("Empty dict")
+if {0:0}:
+    print("Non-empty dict")