class_docstr: Extend Sampler to support "short cycle" sampling.
  See paper "A Multigrid Method for Efficiently Training Video Models",
  Wu et al., 2019 (https://arxiv.org/abs/1912.00998) for details.
code: def __len__(self):
      avg_batch_size = sum(self.batch_sizes) / 3.0
      if self.drop_last:
          return int(np.floor(len(self.sampler) / avg_batch_size))
      else:
          return int(np.ceil(len(self.sampler) / avg_batch_size))
  
imports: import numpy
  import torch
  from torch.utils.data.sampler import Sampler
label_desc: Use image node_id 3 for calling the ShortCycleBatchSampler obj's underlying member method code with example usage: obj.__len__() and returns: int, int