Getting "None" instead of list of values in python

Question

I am currently working on POC on Alibaba Cloud and not authorized to share the information. I am a beginner in python. Let me consider an example to address my issue.

I am getting none instead of list of values,

Example code:

NumSet={1,2,3,4,5,6,7,8,9,10}
NumList = list(NumSet).reverse()
print(NumList)

Output:

None

What I am missing?

the ``.reverse()`` method doesn't return anything, it directly change the list. — iElden, Dec 30 '18 at 14:41
The most pythonic way to reverse a list is `NumList[::-1]`. You don't need any `reverse` or other routines — Sheldore, Dec 30 '18 at 14:43

score 3 · Accepted Answer · answered Dec 30 '18 at 14:41

3

list.reverse() reverses the list in-place and returns nothing (or returns None).

NumList = list(NumSet)  # convert to list first
NumList.reverse()  # reverse in-place

This is the correct way to do it.

answered Dec 30 '18 at 14:41

iBug

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It should also be noted that if you need not-in-place reversal, you can iterate over `reversed(list(NumSet))`. – AKX Dec 30 '18 at 14:43
@AKX What does `set()` in your code do? – iBug Dec 30 '18 at 14:43
Derp, I had misread the set-to-list conversion as being the other way around. Fixed. – AKX Dec 30 '18 at 14:46

score 0 · Answer 2 · answered Dec 30 '18 at 14:46

0

list.reverse() doesn't return the list reversed. What it does is reversing the list in-place. Just change to this and it ill work

NumSet = {1,2,3,4,5,6,7,8,9,10}
NumList = list(NumSet)
NumList.reverse()
print(NumList)

answered Dec 30 '18 at 14:46

Birivera

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Getting "None" instead of list of values in python

2 Answers2