将列表中的所有其他元素相乘 [英] Multiply every other element in a list

问题描述

我有一个列表，例如:list = [6,2,6,2,6,2,6]，我希望它创建一个新列表，其中每个其他元素乘以2，每个其他元素乘以1(保持不变). 结果应为:[12,2,12,2,12,2,12].

I have a list, let's say: list = [6,2,6,2,6,2,6], and I want it to create a new list with every other element multiplied by 2 and every other element multiplied by 1 (stays the same). The result should be: [12,2,12,2,12,2,12].

def multi():
    res = 0
    for i in lst[0::2]:
        return i * 2 

print(multi)

也许是这样，但我不知道该如何进行下去.我的解决方案怎么了?

Maybe something like this, but I don't know how to move on from this. How is my solution wrong?

推荐答案

您可以使用分片分配和列表理解:

You can use slice assignment and list comprehension:

l = oldlist[:]
l[::2] = [x*2 for x in l[::2]]

您的解决方案是错误的，因为:

Your solution is wrong because:

1. 该函数不接受任何参数
2. res被声明为数字而不是列表
3. 您的循环无法知道索引
4. 您在第一次循环迭代中返回
5. 与该功能无关，但您实际上并未调用multi

1. The function doesn't take any arguments
2. res is declared as a number and not a list
3. Your loop has no way of knowing the index
4. You return on the first loop iteration
5. Not related to the function, but you didn't actually call multi

这是您的代码，已更正:

Here's your code, corrected:

def multi(lst):
    res = list(lst) # Copy the list
    # Iterate through the indexes instead of the elements
    for i in range(len(res)):
        if i % 2 == 0:
            res[i] = res[i]*2 
    return res

print(multi([12,2,12,2,12,2,12]))

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