code: def id(expr):
      """
      This is identity optimization.
      :param expr:  expression to optimize
      :return:  a function which always returns expr
      """
  
      def identity(ctx):
          return expr
  
      return identity
  
file_path: h2o-3/h2o-py/h2o/expr_optimizer.py
imports: import h2o.expr
label_desc: Use image node_id 3 for calling a global function with example usage: id(expr) and returns: identity, expr