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問題內容

有人可以解釋一下 python (v3.5) 字典是如何排序的嗎？

data = {"john": 23, "rick": 33, "mary": 63, "ron": 23, "joel": 51}

for key in data:
        print("your name is " + key + ", and you are also " + str(data[key]) + " years old.")

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實際輸出：

your name is rick, and you are also 33 years old.
your name is ron, and you are also 23 years old.
your name is mary, and you are also 63 years old.
your name is john, and you are also 23 years old.
your name is joel, and you are also 51 years old.

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預期輸出（字典的順序）：

Your name is John, and you are also 23 years old.
Your name is Rick, and you are also 33 years old.
Your name is Mary, and you are also 63 years old.
Your name is Ron, and you are also 23 years old.
Your name is Joel, and you are also 51 years old.

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正確答案

這取決于您使用的 Python 版本。

Python 3.6 之前

字典使用底層哈希函數的排序。多種類型具有加鹽哈希，因此這意味著您在每次調用時獲得不同的順序。

Python 3.6+

字典是按插入順序排列的，即字典會記住插入項目的順序。來自文檔：

Python 3.7

Guido van Rossum 在 中宣布從 Python 3.7 開始所有 Python 實現都必須保留插入順序。