new_contents: """
  Given a binary tree, return the postorder traversal of its nodes' values.
  For example:
  Given binary tree {1,#,2,3},
  return [3,2,1]. 
  """
  
  class TreeNode(object):
      def __init__(self, x):
           self.val = x
           self.left = None
           self.right = None
  
  class Solution(object):
      def postorderTraversal(self, root):
          """
          :type root: TreeNode
          :rtype: List[int]
          """
          postorder=[]
          if root:
              postorder.append(root.val)
              if root.right:
                  postorder=self.postorderTraversal(root.right)+postorder
              if root.left:
                  postorder=self.postorderTraversal(root.left)+postorder
              
          return postorder
  
subject: Create BinaryTreePostorderTraversal.py