input: 
  def eval_expr(expr: str) -> float:
      """
      Evaluate a numerical expression given as a string and return the result.
      Example:
      >>> eval_expr("2 + 3 * 4")
      14.0
      >>> eval_expr("(2 + 3) * 4")
      20.0
      """
  
output:     return eval(expr)