这使得当默认值是可变对象时会有所不同，比如列表、字典或者大多数类的实例。
This makes a difference when the default is a mutable object such as a list, dictionary, or instances of most classes.
这使得当默认值是可变对象时会有所不同，比如列表、字典或者大多数类的实例。
This makes a difference when the default is a mutable object such as a list, dictionary, or instances of most classes.
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