temp.py

class Solution:
    def __init__(self):
        self.sum_val = 0

    def _checker(self, root: TreeNode, direction: str):
        if root:
            self._checker(root.left, "left")

            if not root.left and not root.right and direction == "left":
                # print("Adding", root.val, "to", self.sum_val)
                self.sum_val += root.val

            self._checker(root.right, "right")

    def sumOfLeftLeaves(self, root: TreeNode) -> int:
        self._checker(root, "")
        # print("result is", self.sum_val)
        return self.sum_val