code: def _get_storage_freq(self) -> List[str]:
      return sorted(
          set(
              map(
                  lambda x: x.stem.split("_")[0],
                  self.uri.parent.glob("*.txt"),
              )
          )
      )
  
imports: import struct
  from pathlib import Path
  from typing import Iterable, Union, Dict, Mapping, Tuple, List
  import numpy
  import pandas
  from qlib.utils.time import Freq
  from qlib.utils.resam import resam_calendar
  from qlib.config import C
  from qlib.data.cache import H
  from qlib.log import get_module_logger
  from qlib.data.storage import CalendarStorage, InstrumentStorage, FeatureStorage, CalVT, InstKT, InstVT
label_desc: Use image node_id 8 for calling the FileCalendarStorage obj's underlying member method code with example usage: obj._get_storage_freq() and returns: sorted