Get takes two arguments: the dictionary itself, and a key to look up in it.
get使用两个参数：一个是字典本身，另一个是在字典中查找的键。
Each extension should use a unique key to use to store state in the dictionary.
每个扩展需要一个唯一键用于在字典中保存状态。
Each extension should use a unique key to use to store state in the dictionary.
每个扩展需要一个唯一键用于在字典中保存状态。
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