字典的key值判斷或者去除重複的key和value，下面介紹list和set兩種方法：

x={"a":"1","b":"2","c":"3","a":"1","b":"2","c":"3"}或者x={"a":"1","b":"2","c":"3","a":"11","b":"22","c":"33"}都是一樣的；

首先看list方法：

y=list(x)就是["a","b","c"]，這樣得到一個列表並且相同的key也消除了，再看x的值變成這樣了{"a":"11","b":"22","c":"33"}，結果只保留了key處於後面的鍵值對；

再看set方法：

y=set(x)就是set(["a","b","c"

對於list和set方法後的結果都可以取長度，即len(list(x)) 或len(set(x))，得到的都是去重後的key值數量