sys.getsizeof reaturn misleading result

sys.getsizeof for dataclass-based instance return the size of the basic instance structure: PyGC_Head + reference to the type of the instance + refcount + refernce to `__dict__` + refrence to `__weakref__` = 24+8+8+8+8=56. It don't count the space for attribute's values from `__dict__` and the space for `__dict__` instance.