如何替换列表中的元素？

Question

I am trying to write a loop that replaces all the elements of the list with elements that are half a big. If the list is [1,2,3,4] the new list should read [0.5,1,1.5,2]. WITHOUT CREATING A NEW LIST!

I tried the following

for i in Glist:
    i = Glist[i]/2
    Glist.append(i)

And hot an error : list index out of range how to stop the loop?

also tried this:

for i in mylist:
    i = i/2
    mylist.append(i)

did not work

Answer 1

If you want to replace elements of a list, then the length of the list should not change, which append does. Instead:

for i,v in enumerate(Glist):
    Glist[i] = v/2.0

Answer 2

Note that iterating over a list while appending to it is a perfect recipe for an endless loop . Besides iiuc you want to modify the actual elements, here you're just appending to the end of the list.

You could use a regular for loop and just modify in-place with:

for i in range(len(Glist)):
    Glist[i] /= 2.

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print(Glist)
[0.5, 1.0, 1.5, 2.0]