docstr: Tokenizes a text file on character basis.
docstr_tok: ["Tokenizes","a","text","file","on","character","basis","."]
code: def __getitem__(self, index=0) -> torch.Tensor:
      """Tokenizes a text file on character basis."""
      if isinstance(self.files[index], str):
          self.files[index] = Path(self.files[index])
      assert self.files[index].exists()
  
      with self.files[index].open("r", encoding="utf-8") as fin:
          text_lines: Iterable[str] = (
              doc + self.document_delimiter
              for doc in fin.read().split(self.document_delimiter)
              if doc
          )
          if self.random_case_flip:
              text_lines = map(self.random_casechange, text_lines)
          lines = [
              list(line) if self.split_on_char else line.split()
              for line in text_lines
          ]
  
      log.info(f"read text file with {len(lines)} lines")
  
      if self.shuffle:
          random.shuffle(lines)
          log.info("shuffled")
  
      if self.expand_vocab:
          for chars in lines:
              for char in chars:
                  self.dictionary.add_item(char)
  
      ids = torch.tensor(
          [
              self.dictionary.get_idx_for_item(char)
              for chars in lines
              for char in chars
          ],
          dtype=torch.long,
      )
      if not self.forward:
          ids = ids.flip(0)
      return ids
  
imports: import datetime
  import logging
  import math
  import random
  import time
  from pathlib import Path
  from typing import Any, Dict, Iterable, Optional, Type, Union
  import torch
  from torch import cuda
  from torch.optim import AdamW, Optimizer
  from torch.optim.lr_scheduler import ReduceLROnPlateau
  from torch.optim.sgd import SGD
  from torch.utils.data import DataLoader, Dataset
  import flair
  from flair.data import Dictionary
  from flair.models import LanguageModel
  from flair.optim import SGDW, ReduceLRWDOnPlateau
  from flair.training_utils import add_file_handler
label_desc: Use image node_id 3 for calling the TextDataset obj's underlying member method code with example usage: obj.__getitem__(index) and returns: ids