code: def set_symbol_lookup_date(self, dt):
          
          try:
              self._symbol_lookup_date = pd.Timestamp(dt, tz='UTC')
          except ValueError:
              raise UnsupportedDatetimeFormat(input=dt,
                                              method='set_symbol_lookup_date')
docs: Set the date for which symbols will be resolved to their assets
          (symbols may map to different firms or underlying assets at
          different times)
  
          Parameters
          ----------
          dt : datetime
              The new symbol lookup date.