input: def evaluate_expression(expr: str) -> float:
      """
      Evaluate a string containing a numerical expression and return the result.
      
      >>> evaluate_expression("2 + 2")
      4.0
      >>> evaluate_expression("5 * (3 + 4)")
      35.0
      >>> evaluate_expression("10 / 2")
      5.0
      """
      return eval(expr)
output:     return eval(expr)