comefrom: <qiyuangong>144_Binary_Tree_Preorder_Traversal_1.py
code: def preorderTraversal( root):
      if root is None:
          return []
      res = []
      stack = [root]
      while len(stack) > 0:
          curr = stack.pop()
          res.append(curr.val)
          if curr.right is not None:
              stack.append(curr.right)
          if curr.left is not None:
              stack.append(curr.left)
      return res
masked: def sample_funcname ( var_0 ) :
      if var_0 is None :
          return [ ]
      var_2 = [ ]
      var_3 = [ var_0 ]
      while len ( var_3 ) > 0 :
          var_7 = var_3.pop ( )
          var_2.append ( var_7.val )
          if var_7.right is not None :
              var_3.append ( var_7.right )
          if var_7.left is not None :
              var_3.append ( var_7.left )
      return var_2
  