字典（dic）//我觉得是列表的另一种用法，只是用列表比较麻烦，可以用字典来简化,元素采用key-value对应方法，删除key时对应的值也会被删除
>>>dic = {"Tom":85,"Jhon":70,"Linda":90}
>>>print dic
{"Tom":85,"Jhon":70,"Linda":90}
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查询某个元素是否在字典中时
(1)>>> "Tom" in dic
True
>>>"Jam" in dic
False
(2)>>>dic.get("Tom")
85
>>>dic.get("Jam") //不会返回值，或者自定义值：dic.get("Jam",-1)不存在返回-1
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>>>dic.pop('Tom')
85
>>>print dic
{"Jhon":70,"Linda":90}
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