code: def __len__(self) -> int:
      return self._length
  
file_path: pytorch-lightning/src/lightning/data/streaming/sampler.py
imports: import logging
  from dataclasses import dataclass
  from typing import Any, Dict, Iterator, List, Optional, Union
  import numpy
label_desc: Use image node_id 9 for calling the CacheBatchSampler obj's underlying member method code with example usage: obj.__len__() and returns: self