How to turn all numbers in a list into their negative counterparts?

Question

I am trying to turn a list of positive numbers into a list of negative numbers with the same value in python 3.3.3

For example turning [1,2,3] into

Answer 1

There is also this method:

Little note, this will only work if all numbers start positive. It won't affect 0. If you have negative numbers you don't want changing you need to add the IF statement below.

if num < 0: continue
numbers = [1, 2, 3, 4 ,5]
for num in numbers:
    numbers[num-1] = num - (2*num)

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numbers
[-1, -2, -3, -4, -5]