class_docstr: The partition sampler given a DGLGraph and partition number.
  The metis is used as the graph partition backend.
class_docstr_tok: ["The","partition","sampler","given","a","DGLGraph","and","partition","number",".","The","metis","is","used","as","the","graph","partition","backend","."]
code: def __len__(self):
      return self.psize
  
file_path: dgl/examples/pytorch/ogb/cluster-sage/sampler.py
imports: import os
  import random
  import time
  import torch
  from partition_utils import *
  import dgl.function
label_desc: Use image node_id 3 for calling the ClusterIter obj's underlying member method code with example usage: obj.__len__() and returns: self