code: def _fetch(self, index: int) -> Tuple[TimeSeries, slice, slice]:
      scope_id, tgt_head = self.windows[index]
      tgt_tail = tgt_head + self.horizon
      ctx_tail = tgt_head - self.gap
      ctx_head = (
          None if self.context is None else ctx_tail - self.context
      )
      ctx_window = slice(ctx_head, ctx_tail)
      tgt_window = slice(tgt_head, tgt_tail)
      return self.corpus[scope_id], ctx_window, tgt_window
  
file_path: gluonts/src/gluonts/nursery/daf/tslib/dataset/forecasting.py
imports: from __future__ import annotations
  from typing import List, Tuple, Dict, Optional
  import numpy
  from tqdm import tqdm
  from .timeseries import TimeSeries, TimeSeriesCorpus
  from .windows import WindowsDataset
label_desc: Use image node_id 3 for calling the ForecastingDataset obj's underlying member method code with example usage: obj._fetch(index) and returns: self,  ctx_window,  tgt_window