我们用高速缓存阶乘计算器factorial . py作为类定义的练习，如清单4所示。

For an exercise in class definition, you'll use the caching factorial calculator of factorial.py, shown in Listing 4.

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这里是一个阶乘计算器的实现，我们会使用一种常规的方法，通过调用第二个，嵌套的方法来完成计算。

Here is an implementation of a factorial calculator, where we use a conventional technique of calling a second, nested method to do the work.

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