input: 
  def eval_expr(expr: str) -> float:
      """Given a string containing a numerical expression, returns the result of the evaluation.
      >>> eval_expr("2 + 3 * 4")
      14
      >>> eval_expr("(2 + 3) * 4")
      20
      >>> eval_expr("10 / 2 + 3")
      8.0
      """
  
output:     return eval(expr)