def METHOD_NAME(code_str):
  arena = test_lib.MakeArena('<arith_parse_test.py>')
  w_parser, _ = parse_lib.MakeParserForCompletion(code_str, arena)
  anode = w_parser._ReadArithExpr()  # need the right lex state?
  if not anode:
    raise ExprSyntaxError("failed %s" % w_parser.Error())
  print('node:', anode)
  mem = state.Mem('', [], {}, None)
  exec_opts = state.ExecOpts(mem)
  splitter = legacy.SplitContext(mem)
  ev = word_eval.CompletionWordEvaluator(mem, exec_opts, splitter)
  arith_ev = expr_eval.ArithEvaluator(mem, exec_opts, ev)
  value = arith_ev.Eval(anode)
  return value