failed to add 1 to an integer list using for loop

Asked Jun 23 '21 at 09:27

Active Jun 23 '21 at 09:27

Viewed 21 times

As a new python learner, I'm quite confused about why the list_2 output isn't[2,4,6,8,10]

list_1=[[1,3],[3,4],[5,8]]
for x in list_1:
    x[0]=1
print(list_1)

list_2=[1,3,5,7,9]
for x in list_2:
    x=x+1
print(list_2)

Output

[[1, 3], [1, 4], [1, 8]]
[1, 3, 5, 7, 9]

asked Jun 23 '21 at 09:27

Des1gnWizard

you are changing the number not assigning it back to the list – Abhishek Jun 23 '21 at 09:29
Please see https://nedbatchelder.com/text/names1/names1.html and specifically page 18. – Mustafa Aydın Jun 23 '21 at 09:30
how to assign the new value to the list element without using list comprehension – Des1gnWizard Jun 23 '21 at 09:30
1

There are some good answers on [Do Python for loops work by reference?](https://stackoverflow.com/q/14814771/5358968) – Steve Jun 23 '21 at 09:31
Thank you guys so much. I will look into the reference. – Des1gnWizard Jun 23 '21 at 09:33
@Abhishek they aren't *changing the number*, they are creating *new numbers* – juanpa.arrivillaga Jun 23 '21 at 09:34
1

One way You could do it with a list compression is `for i, x in enumerate(list_2): list2[i] = x+1` – Steve Jun 23 '21 at 09:34

0 Answers0