human
Solve the following python programming problem given the following code:
# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        ans = []
        if root is None:
            return ans
        
        # iterative
        stack = []
        while True:
            while root:
                stack.append(root)
                root = root.left
            if not stack:
                return ans
            node = stack.pop()
            ans.append(node.val)
            root = node.right
        
        # recursive 
        return self.inorderTraversal(root.left) + [root.val] + self.inorderTraversal(root.right)
        
Given the above code, generate some markdown instructions for it.
assistant
#Here is the Python program you requested.

Binary Tree Inorder Traversal

https://leetcode.com/problems/binary-tree-inorder-traversal/#/description
Given a binary tree, return the inorder traversal of its nodes' values.
For example:
Given binary tree [1,null,2,3],
   1
    \
     2
    /
   3
return [1,3,2].
Note: Recursive solution is trivial, could you do it iteratively?