Kth Smallest Element in a BST

def kthSmallest(root, k):
    stack = []
    curr = root
    
    while stack or curr:
        while curr:
            stack.append(curr)
            curr = curr.left
            
        curr = stack.pop()
        k -= 1
        if k == 0:
            return curr.val
            
        curr = curr.right