code: def __init__(self, N):
      self.captions = [
          str(uuid4())[: np.random.randint(50)] for _ in range(N)
      ]
  
file_path: ffcv/tests/test_custom_field.py
imports: import pytest
  import numpy
  from uuid import uuid4
  from ffcv.fields.ndarray import NDArrayField, NDArrayDecoder
  from ffcv.writer import DatasetWriter
  from ffcv.loader import Loader, OrderOption
  from tempfile import NamedTemporaryFile
label_desc: Use image node_id 1 to create a new CaptionDataset object  with example: obj = CaptionDataset(N)