code: def __getitem__(self, i):
      return self.dataset[i][self.key]
  
imports: import numpy
  import torch
  from torch.utils.data import Dataset, IterableDataset
  from ..utils.generic import ModelOutput
label_desc: Use image node_id 3 for calling the KeyDataset obj's underlying member method code with example usage: obj.__getitem__(i) and returns: self