Python error while using global variable. Name is not defined

Question

When I'm trying to use res variable in my ft_helper function it gives me error Name is not defined. As you could see I do tell that res variable is global. How do I do in python that variable is available and could be changed in nested functions. More clear in a picture is it because of recursion ?? code:

class Solution:
    def minOperations(self, nums: List[int], x: int) -> int:
        res = -1
        
        def ft_helper(nums, x, pl, pr):
            global res
            
            if x == 0:
                res = pl + pr if res == -1 else  min(pl + pr, res) //error, res name is not defined
                return 
            if(pl >= len(nums) or pr < 0): return
            ft_helper(nums, x = x - nums[pl], pl = pl + 1, pr = pr)
            ft_helper(nums, x = x - nums[pr], pl = pl, pr = pr - 1)
        ft_helper(nums, x, pl = 0, pr = len(nums) - 1)
        return res

Answer 1

The solution is simply to replace global res with nonlocal res.

The variable res is not a global variable as it's defined within the scope of minOperations. It is not a local variable (from ft_helper's point-of-view) as it's not defined within ft_helper's scope. Instead it is considered a nonlocal variable from ft_helper's point-of-view.

It you look at PEP 3104, you will see that nonlocal was proposed precisely for situations like yours (accessing non-global variables from outer scopes).