将函数映射到字典中指定键的值 [英] Map a function to values of specified keys in dictionary

问题描述

是否有方便的方法将功能映射到字典中的指定键？

Is there a convenient way to map a function to specified keys in a dictionary?

即给定

d = {"a": 1, "b": 2, "c": 3}

想将一个函数（例如f）映射到键 a和 c：

would like to map a function, say f, to keys "a" and "c":

{"a": f(1), "b": 2, "c": f(3)}

编辑

正在寻找不会更新输入字典的方法。

Looking for methods that will not update the input dictionary.

推荐答案

您可以使用字典理解：

output_dict = {k: f(v) for k, v in d.items()}

f（v）将被立即求值（调用），其返回值将作为字典的值存储。

Note that f(v) will be evaluated (called) immediately and its return values will be stored as the dictionary's values.

如果要存储该函数并在以后调用它（已存储参数），则可以使用 functools.partial ：

If you want to store the function and call it later (with the arguments already stored) you can use functools.partial:

from functools import partial


def f(n):
    print(n * 2)


d = {"a": 1, "b": 2, "c": 3}

output_dict = {k: partial(f, v) for k, v in d.items()}

output_dict['b']()
# 4

如果您只想要特定键映射后，您当然不能使用 .items 并仅覆盖这些键：

If you only want specific keys mapped you can of course not use .items and just override those keys:

d['a'] = partial(f, d['a'])

或更为笼统的

keys = ('a', 'c')
for key in keys:
    d[key] = partial(f, d[key])

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