input: def eval_expr(expr: str) -> float:
      """ Evaluates a numerical expression given as a string and returns the result.
      >>> eval_expr("5 + 3 * 2")
      11.0
      >>> eval_expr("(5 + 3) * 2")
      16.0
      >>> eval_expr("10 / 2 - 1")
      4.0
      """
output:     return eval(expr)