code: def normalize_symbol(self, symbol: str) -> str:
      symbol, exchange = symbol.split(".")
      exchange = "sh" if exchange == "ss" else "sz"
      return f"{exchange}{symbol}"
  
imports: import re
  import sys
  from datetime import datetime
  from pathlib import Path
  from typing import List, Iterable, Optional, Union
  import fire
  import pandas
  import baostock
  from loguru import logger
  from data_collector.base import BaseCollector, BaseRun, BaseNormalize
  from data_collector.utils import get_hs_stock_symbols, get_calendar_list
label_desc: Use image node_id 3 for calling the PitCollector obj's underlying member method code with example usage: obj.normalize_symbol(symbol) and returns: exchange, symbol