input: 
  def eval_expr(expr: str) -> float:
      """Evaluate a given numerical expression as a string and return the result.
      >>> eval_expr("2+2")
      4.0
      >>> eval_expr("5*3-2")
      13.0
      >>> eval_expr("10/2+3")
      8.0
      """
      return eval(expr)
  
output:     try:
          result = eval(expr)
          return float(result)
      except Exception as e:
          raise ValueError(f"Invalid expression: {expr}")