code: def __getitem__(
      self, i: Union[int, slice]
  ) -> Union[Tuple[int, float], pd.Series]:
      if not self.uri.exists():
          if isinstance(i, int):
              return None, None
          elif isinstance(i, slice):
              return pd.Series(dtype=np.float32)
          else:
              raise TypeError(f"type(i) = {type(i)}")
  
      storage_start_index = self.start_index
      storage_end_index = self.end_index
      with self.uri.open("rb") as fp:
          if isinstance(i, int):
              if storage_start_index > i:
                  raise IndexError(
                      f"{i}: start index is {storage_start_index}"
                  )
              fp.seek(4 * (i - storage_start_index) + 4)
              return i, struct.unpack("f", fp.read(4))[0]
          elif isinstance(i, slice):
              start_index = (
                  storage_start_index if i.start is None else i.start
              )
              end_index = (
                  storage_end_index if i.stop is None else i.stop - 1
              )
              si = max(start_index, storage_start_index)
              if si > end_index:
                  return pd.Series(dtype=np.float32)
              fp.seek(4 * (si - storage_start_index) + 4)
              # read n bytes
              count = end_index - si + 1
              data = np.frombuffer(fp.read(4 * count), dtype="<f")
              return pd.Series(
                  data, index=pd.RangeIndex(si, si + len(data))
              )
          else:
              raise TypeError(f"type(i) = {type(i)}")
  
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 7 for calling the FileFeatureStorage obj's underlying member method code with example usage: obj.__getitem__(i) and returns: None,  None, i,  struct, pd, pd, pd