※ 引述《renshin (阿信)》之铭言： : 请问要如何用dict中的value找key呢? : 例如有个dict : d = {'a':'100', 'b':'200', 'c':'200', 'd':'100', 'e':'150'} : 想把带有相同value的key集合起来成各自一个list : 或者可能形成一个新的dict，如 : Newd = {'100':['a','d'], '150':'e', '200':['b','c']} : 请问有大大可以教一下新手小嫩吗? : 谢谢 用 for 去遍历 dict 中的 key 跟 value 就可以了 ```python # declare the result dict to store reversed dict result = {} # traverse original dict d = {'a': '100', 'b': '200', 'c': '200', 'd': '100', 'e': '150'} for k, v in d.items(): result.setdefault(v, list()).append(k) ``` --- 顺带一提，这边用的 setdefault() 跟我写的这篇 #1T-Uj77Q (Python) 用到的 defaultdict 是还满异曲同工的东西 可以让你的代码写起来更加地 pythonic 一点 不过建议使用 defaultdict 会更好一些 > It would make sense that defaultdict is faster that dict.setdefault() > since the former sets its default for the entire dict at creation time, > whereas setdefault() does it per element when it is read. One reason to > use setdefault is when the default you assign is based on the key (or > something) rather than a generic default for the entire dict. # References 提升逼格的两个函数：setdefault 与 defaultdict https://bit.ly/2Mtgj7N setdefault vs defaultdict performance https://bit.ly/2Md9Ayw --

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