如何将嵌套字典中每个键的所有值提取到列表中（Python）

你现有的代码可以实现需求，但确实有更简洁、贴合Python风格的写法，下面给出几种优化方案：

原代码 #

if __name__ == "__main__":

    master_dict = {"1": {"1": 11, "2":22, "3": 33},
                   "2": {"1": 15, "2":23, "3": 31}}

    ones = []
    twenties = []
    thirties = []
    for k, v in master_dict.items():
        ones.append(v["1"])
        twenties.append(v["2"])
        thirties.append(v["3"])

    print("ones : ", ones)
    print("twenties : ", twenties)
    print("thirties : ", thirties)

原运行结果 #

ones :  [11, 15]
twenties :  [22, 23]
thirties :  [33, 31]

方案1：列表推导式（最简洁直观） #

用列表推导式直接生成目标列表，省去循环内的append操作，代码更紧凑：

if __name__ == "__main__":
    master_dict = {"1": {"1": 11, "2":22, "3": 33},
                   "2": {"1": 15, "2":23, "3": 31}}

    ones = [v["1"] for v in master_dict.values()]
    twenties = [v["2"] for v in master_dict.values()]
    thirties = [v["3"] for v in master_dict.values()]

    print("ones : ", ones)
    print("twenties : ", twenties)
    print("thirties : ", thirties)

这里直接遍历master_dict.values()（不需要外层字典的键，所以不用items()），一行代码生成一个列表，符合Python的简洁风格。

方案2：单次遍历生成所有列表 #

如果担心多次遍历字典（虽然开销极小），可以用一次循环同时填充三个列表，兼顾效率和简洁性：

if __name__ == "__main__":
    master_dict = {"1": {"1": 11, "2":22, "3": 33},
                   "2": {"1": 15, "2":23, "3": 31}}

    ones, twenties, thirties = [], [], []
    for v in master_dict.values():
        ones.append(v["1"])
        twenties.append(v["2"])
        thirties.append(v["3"])

    print("ones : ", ones)
    print("twenties : ", twenties)
    print("thirties : ", thirties)

把三个列表的初始化放在一行，同时遍历values()，比原代码更紧凑。

方案3：用zip批量提取 #

如果嵌套字典的键顺序固定，可通过zip一次性提取所有对应位置的值，代码量最少：

if __name__ == "__main__":
    master_dict = {"1": {"1": 11, "2":22, "3": 33},
                   "2": {"1": 15, "2":23, "3": 31}}

    # 按固定顺序取出子字典的值，再用zip打包分组
    ones, twenties, thirties = zip(*((v["1"], v["2"], v["3"]) for v in master_dict.values()))
    # zip返回元组，转成列表（如果需要的话）
    ones, twenties, thirties = list(ones), list(twenties), list(thirties)

    print("ones : ", ones)
    print("twenties : ", twenties)
    print("thirties : ", thirties)

注：Python 3.7+中字典的values()会保留插入顺序，如果你的版本低于3.7，必须显式指定键的顺序（如上代码），避免值的顺序混乱。

内容的提问来源于stack exchange，提问作者Windy71