code: def __getitem__(
      self, i: Union[int, slice]
  ) -> Union[Tuple[int, float], pd.Series]:
      df = self._data
      storage_start_index = df.index[0]
      storage_end_index = df.index[-1]
      if isinstance(i, int):
          if storage_start_index > i or i > storage_end_index:
              raise IndexError(
                  f"{i}: start index is {storage_start_index}"
              )
          data = self.data[i]
          return i, data
      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
          si = max(start_index, storage_start_index)
          if si > end_index or self.field not in df.columns:
              return pd.Series(dtype=np.float32)  # type: ignore
          data = df[self.field].tolist()
          result = data[
              si - storage_start_index : end_index - storage_start_index
          ]
          return pd.Series(result, index=pd.RangeIndex(si, si + len(result)))  # type: ignore
      else:
          raise TypeError(f"type(i) = {type(i)}")
  
imports: from typing import Union, List, Dict, Tuple
  import unittest
  import pandas
  import numpy
  import io
  from .data import GetData
  from ..None import init
  from ..constant import REG_CN, REG_TW
  from qlib.data.filter import NameDFilter
  from qlib.data import D
  from qlib.data.data import Cal, DatasetD
  from qlib.data.storage import CalendarStorage, InstrumentStorage, FeatureStorage, CalVT, InstKT, InstVT
label_desc: Use image node_id 5 for calling the MockFeatureStorage obj's underlying member method code with example usage: obj.__getitem__(i) and returns: i,  data, pd, pd