Keep your inheritance hierarchy simple.
保持简单的继承层次结构。
The reason is simple: The module has an inheritance hierarchy of its own.
原因很简单：模型具有自己的继承层次结构。
We need two new Classes at either end of the inheritance hierarchy to do this.
在继承层次的每个端点，我们需要两个新类来完成这个。
We need two new Classes at either end of the inheritance hierarchy to do this.
在继承层次的每个端点，我们需要两个新类来完成这个。
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