code: def is_tuple(node):
      
      if isinstance(node, Node) and node.children == [LParen(), RParen()]:
          return True
      return (isinstance(node, Node)
              and len(node.children) == 3
              and isinstance(node.children[0], Leaf)
              and isinstance(node.children[1], Node)
              and isinstance(node.children[2], Leaf)
              and node.children[0].value == u"("
              and node.children[2].value == u")")
docs: Does the node represent a tuple literal?