code: def size(self):
      return len(self.flows)
  
file_path: tensorpack/examples/OpticalFlow/flownet2.py
imports: import argparse
  import glob
  import os
  import cv2
  from tensorpack import *
  from tensorpack.utils import viz
  import flownet_models
  from helper import Flow
label_desc: Use image node_id 2 for calling the SintelData obj's underlying member method code with example usage: obj.size() and returns: len