Apply suggestion from @serhiy-storchaka

Author: serhiy-storchaka

Lib/unittest/mock.py

@@ -798,8 +798,7 @@ def __dir__(self):
         from_type = [e for e in from_type if not e.startswith('_')]
         from_dict = [e for e in from_dict if not e.startswith('_') or
                      _is_magic(e)]
-        return sorted(set(list(extras) + from_type + from_dict +
-                          from_child_mocks))
+        return sorted({*extras, *from_type, *from_dict, *from_child_mocks})
 
 
     def __setattr__(self, name, value):