Suppose I have a list nums = [1,3,2,5,6] and I want to subtract each element's value by 1. Now I wrote codes like
for i in nums:
i -= 1
However, when I print nums its values did not change. I'm wondering why it doesn't work, and whether there is an elegant way in Python to do this. Thank you!
i is a local variable and does not reflect the actual objects in nums, only their values. The best way to do this is to use a list comprehension:
nums = [i - 1 for i in nums]
If you need to retain references to nums:
nums[:] = = [i - 1 for i in nums]
Demo:
>>> nums = [1, 2, 3]
>>> [i - 1 for i in nums]
[0, 1, 2]
The for loop sets i to successive values in the list, not references into the list. There are a couple ways to accomplish what you want:
nums = [i-1 for i in nums]
Is one way. If you need to keep the same list object you could do:
for ndx in xrange(len(nums)):
nums[ndx] -= 1
