code: def __len__(self):
      return len(self.traversal_order.indices)
  
imports: from typing import Any, Callable, List, Mapping, Optional, Sequence, Type, Union
  import warnings
  from ffcv.fields.base import Field
  import torch
  from torch.utils.data.sampler import BatchSampler, Sampler
  from ffcv.loader.loader import Loader, OrderOption, ORDER_TYPE, DEFAULT_OS_CACHE
  from ffcv.traversal_order.base import TraversalOrder
  from ffcv.pipeline.operation import Operation
  from ffcv.pipeline import Compiler
  from avalanche.benchmarks.utils.ffcv_support.ffcv_epoch_iterator import _CustomEpochIterator
label_desc: Use image node_id 3 for calling the _TraversalOrderAsSampler obj's underlying member method code with example usage: obj.__len__() and returns: len