class_docstr: Wraps the MSCOCO datasets and is used by the iterator to fetch data.
class_docstr_tok: ["Wraps","the","MSCOCO","datasets","and","is","used","by","the","iterator","to","fetch","data","."]
code: def __len__(self):
      return len(self.anns)
  
file_path: chainer/examples/image_captioning/datasets.py
imports: from collections import defaultdict
  import os
  import numpy
  from PIL import Image
  from pycocotools.coco import COCO
  from chainer import dataset
  from chainer.dataset.convert import to_device
label_desc: Use image node_id 2 for calling the MsCocoDataset obj's underlying member method code with example usage: obj.__len__() and returns: len