如何在不更改列表的情况下更改列表内的值（Python）

Question

How do you change a value from positive to negative inside a list when you need it, without changing list itself.

Example(sorry will be a bit of Maya, but i think even people who doesn't know Maya will get it) :

someList = [1.7, 18.9, -0.3]
cmds.joint(n="test", p=someList)

and I want in this case, someList = [-1.7, 18.9, -0.3] - "1.7" make negative.

So I was wondering if there is a way to make it without creating different list or changing existing one?

Answer 1

someList[0] = -someList[0]

where 0 is index. If you don't know index and just value say 1.7

indx = someList.index(1.7)
someList[indx] = -someList[indx]

Answer 2

您可以重新初始化相同的索引

someList[0]=-someList[0]

Answer 3

If you don't want to change someList , you can try this:

someList = [1.7, 18.9, -0.3]
cmds.joint(n="test", p=[-someList[0]] + someList[1:])

It makes 1.7 negative and concatenates it to the rest of the someList .

Answer 4

This is job for list comprehension. Multiply by (-1) on the fly:

for x in [[x*-1] for x in someList]:
    print(x)

Output:

[-1.7]
[-18.9]
[0.3]