new_contents: # Definition for a binary tree node.
  # class TreeNode:
  #     def __init__(self, x):
  #         self.val = x
  #         self.left = None
  #         self.right = None
  
  class Solution:
      # @param {TreeNode} root
      # @return {boolean}
      def isSym(self, l, r):
          if l == None and r != None:
              return False
          if l != None and r == None:
              return False
          if l == None and r == None:
              return True
          if l.val != r.val:
              return False
          return self.isSym(l.left, r.right) & self.isSym(l.right, r.left)
          
      def isSymmetric(self, root):
          if root == None:
              return True
              
          return self.isSym(root.left, root.right)
  
subject: Create SymmetricTree_001.py