docstr: return the latest trading date for user {user_id}
      Parameter
          user_id : string
      :return
          date : string (e.g '2018-10-08')
docstr_tok: ["return","the","latest","trading","date","for","user","{","user_id","}","Parameter","user_id",":","string",":","return","date",":","string","(","e.g","'2018-10-08","'",")"]
code: def get_latest_trading_date(self):
      """
      return the latest trading date for user {user_id}
          Parameter
              user_id : string
          :return
              date : string (e.g '2018-10-08')
      """
      if not self.account.last_trade_date:
          return None
      return str(self.account.last_trade_date.date())
  
file_path: qlib/qlib/contrib/online/user.py
imports: import logging
  from ...log import get_module_logger
  from ..evaluate import risk_analysis
  from ...data import D
label_desc: Use image node_id 3 for calling the User obj's underlying member method code with example usage: obj.get_latest_trading_date() and returns: str, None