常常可以发现bug的原因是调用者发送了类型错误的参数或数量错误的参数，或者实际参数和形式参数的次序不匹配。

Often, you can trace the origin of a bug back to a caller that's sending the wrong type of argument, the wrong number of arguments, or a mismatch between the order of actual and formal arguments.

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也能提醒实际参数和形式参数的使用过程：调用一个函数的时候，把实际参数的值赋给了形式参数。

It is also a reminder about how arguments and parameters work: when you call a function, the arguments are assigned to the parameters.

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实际参数：当函数被调用的时候，提供给函数的值。这个值会被函数接收，赋给函数内部的形式参数。

A value provided to a function when the function is called. This value is assigned to the corresponding parameter in the function.

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