Python字典理解示例 [英] Python dictionary comprehension example

问题描述

我正在尝试学习Python字典理解，我认为有可能在一行中做以下功能。我不能像第一个那样使 n + 1 ，或者避免使用 range（）

I am trying to learn Python dictionary comprehension, and I think it is possible to do in one line what the following functions do. I wasn't able to make the n+1 as in the first or avoid using range() as in the second.

是否可以使用在理解期间自动递增的计数器，如 test1（）？

Is it possible to use a counter that automatically increments during the comprehension, as in test1()?

def test1():
    l = ['a', 'b', 'c', 'd']
    d = {}
    n = 1
    for i in l:
        d[i] = n
        n = n + 1
    return d

def test2():
    l = ['a', 'b', 'c', 'd']
    d = {}
    for n in range(len(l)):
        d[l[n]] = n + 1
    return d

推荐答案

使用 枚举 功能：

>>> L = ['a', 'b', 'c', 'd']
>>> {letter: i for i,letter in enumerate(L, start=1)}
{'a': 1, 'c': 3, 'b': 2, 'd': 4}

请注意，如果您想要反向映射，即映射 1 to a ， 2 to b etc，you可以简单地做：

Note that, if you wanted the inverse mapping, i.e. mapping 1 to a, 2 to b etc, you could simply do:

>>> dict(enumerate(L, start=1))
{1: 'a', 2: 'b', 3: 'c', 4: 'd'}

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