Python列表解析 [英] Python List Comprehensions

问题描述

我正在学习python3列表理解.我了解如何格式化列表理解:[等式，for循环，如果要过滤的if语句]，但是我无法弄清楚如何将三行代码浓缩为等式"部分的单个等式.

I am learning python3 list comprehensions. I understand how to format a list comprehension: [equation, for loop, if statement for filtering], but I cannot figure out how to condense three lines of code into a single equation for the 'equation' part.

我要获取一个数字并将其添加到自身中，然后获取结果并将其添加到自身中，以此类推，以在列表中创建一个数字序列.

I am taking a number and adding it to itself and then taking the result and adding it to itself and so on to create a sequence of numbers in the list.

我可以通过声明x = 1然后循环执行以下操作来实现此目的:

I can accomplish this by declaring x = 1 and then looping the following:

y = x + x

y = x + x

x = y

有人可以帮我把它变成单线方程式吗?如果可能的话，我将来可以学习以帮助我解决这一问题的资源吗?

Can anybody help me to turn this into a single-lined equation and if possible, resources that I might study to help me with this in the future?

推荐答案

您的算法等效于乘以2的幂:

Your algorithm is equivalent to multiplying by powers of 2:

x = 3
res = [x * 2**i for i in range(10)]

# [3, 6, 12, 24, 48, 96, 192, 384, 768, 1536]

要了解为什么是这种情况，请注意，在 for 循环的每次迭代中，您都将起始数字乘以2:

To see why this is the case, note you are multiplying your starting number by 2 in each iteration of your for loop:

x = 3
res = [x]
for _ in range(9):
    y = x + x
    x = y
    res.append(y)

print(res)

# [3, 6, 12, 24, 48, 96, 192, 384, 768, 1536]

正如@timgeb所提到的，您不能随便引用列表理解的元素，因为在理解完成之前这些元素不可用.

As @timgeb mentions, you can't refer to elements of your list comprehension as you go along, as they are not available until the comprehension is complete.

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