comefrom: <doocs>0226.Invert Binary Tree_1.py
code: def dfs(root):
      if root is None:
          return
      root.left, root.right = root.right, root.left
      dfs(root.left)
      dfs(root.right)
masked: def sample_funcname ( var_1 ) :
      if var_1 is None :
          return
      var_1.left , var_1.right = var_1.right , var_1.left
      var_0 ( var_1.left )
      var_0 ( var_1.right )
  