input: 
  def eval_expression(expr: str) -> float:
      """Evaluates a given string containing a numerical expression and returns the result.
      >>> eval_expression("3 + 5")
      8
      >>> eval_expression("10 * 2 - 1")
      19
      """
  
output:     try:
          return float(eval(expr))
      except:
          raise ValueError("Invalid expression")