code: def __getitem__(self, i):
      chunk = self.data[i : i + self.block_size + 1]
      dix = [self.stoi[s] for s in chunk]
  
      # src and target are off by one, we want the model to predict the next word
      x = torch.tensor(dix[:-1], dtype=torch.long)
      y = torch.tensor(dix[1:], dtype=torch.long)
      return x, y
  
imports: import math
  import os
  import pytorch_lightning
  import torch
  import torch.nn
  from pytorch_lightning import Trainer, seed_everything
  from pytorch_lightning.utilities import rank_zero_info
  from torch.nn import functional
  from torch.utils.data import DataLoader, Dataset, RandomSampler
  from xformers.factory.model_factory import xFormer, xFormerConfig
label_desc: Use image node_id 3 for calling the CharDataset obj's underlying member method code with example usage: obj.__getitem__(i) and returns: x,  y