code: def bench_start_date(self) -> pd.Timestamp:
      return pd.Timestamp("2007-01-15")
  
imports: import re
  import abc
  import sys
  from io import BytesIO
  from typing import List, Iterable
  from pathlib import Path
  import fire
  import requests
  import pandas
  import baostock
  from tqdm import tqdm
  from loguru import logger
  from data_collector.index import IndexBase
  from data_collector.utils import get_calendar_list, get_trading_date_by_shift, deco_retry
  from data_collector.utils import get_instruments
label_desc: Use image node_id 2 for calling the CSI500Index obj's underlying member method code with example usage: obj.bench_start_date() and returns: pd