Another reason is that by passing a DictionaryIO object to Dictionary, you can take advantage of class switching, or polymorphism.

另一个原因是通过将DictionaryIO对象传递给Dictionary，可以利用类切换或多态性。

youdao

It stands to benefit from a rising middle class that is switching from the harsh, hand-rolled cigarettes sold individually by street vendors.

FORBES: Bad government, good companies