前置条件和后置条件方法可以看到作为函数参数 （ args） 传递的值。
The pre-condition and post-condition methods can also see the values passed as function arguments (args).
请注意，它是一个非常简单的类，几乎所有函数都有前置条件。
Please note that this is a very simple class, with preconditions on almost all its functions.
前置条件：函数开始之前，调用者应当满足的要求。
A requirement that should be satisfied by the caller before a function starts.
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