CODEWITHSUNDEEP
python
Ayush Bisht
Ayush Bisht

Reputation: 5

scope of variable within a function in python

While trying to solve a problem on leetcode, I ran into an error "local variable referenced before assignment". Below I have given the entire code (the logic of the code itself is not my question). I have defined the variable within the outer function. I read somewhere, that in python, the scope of a variable works in this way - the variable is first searched locally, then in outer functions (if there are any), then global. In my code, no local variable "total" exists, but there is one defined in the outer function. Is my understanding of scope of variables wrong? Also, I used something similar in another problem but instead of an integer, I was using a list, which was similarly defined in the outer function only, and being appended in the inner function. In this case, no such error occurred. What I am doing wrong here? Any clarification is greatly appreciated. 

class Solution:
    def pathSum(self, root: TreeNode, sum: int) -> int:
        total = 0
        if root is None:
            return 0

        def helper(root, sum, rem):
            if root is None:
                return 


            if root.val == rem:
                total += 1

            if root.left is not None:
                helper(root.left, sum, sum - root.val)    

            if root.right is not None:
                helper(root.right, sum, sum - root.val)

            return 

        helper(root, sum, sum)

        return total
'''

Upvotes: 0

Views: 121

Answers (1)

Ed Ward
Ed Ward

Reputation: 2331

To fix this, use a nonlocal declaration:

class Solution:
    def pathSum(self, root: TreeNode, sum: int) -> int:
        total = 0
        if root is None:
            return 0

        def helper(root, sum, rem):
            nonlocal total
            if root is None:
                return 


            if root.val == rem:
                total += 1

            if root.left is not None:
                helper(root.left, sum, sum - root.val)    

            if root.right is not None:
                helper(root.right, sum, sum - root.val)

            return 

        helper(root, sum, sum)

        return total

Essentially, total += 1 implicitly tells Python that total is a local variable.

Have a look at this answer

Upvotes: 1

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