Why can I sometimes edit some list variables with inner function, but not ints in Python

Question

For example, if I use the following code, this will not change nums value

def K():
    nums = 4
    def helper(x):
        nums = 
    helper(3)
    return nums
print(K())

# 4 -> 4

However, if nums is a list, I can

def K():
    nums = [0]
    def helper(x):
        nums[0] = x 
    helper(3)
    return nums
print(K())

# [0] -> [3]

First of all, you're not doing anything with `nums = ` in the _helper_ function on the first example. Is that the same on your actual code? — Prav, Dec 30 '21 at 01:43

score 1 · Answer 1 · answered Dec 30 '21 at 02:01

In the first example, you're actually creating a variable called nums that only lives inside your function helper

In the second example, helper is editing an existing list from the outer scope.

It's just how scopes work for different elements in Python. Variables from the outer scope are as good as read-only. You can read more here.

1 Answers1