class_docstr: Graph Dataloader
      
class_docstr_tok: ["Graph","Dataloader"]
docstr: batch_fn batch producer
docstr_tok: ["batch_fn","batch","producer"]
code: def batch_fn(self, batch_examples):
      """batch_fn batch producer"""
      graphs = [b[0] for b in batch_examples]
      labels = [b[1] for b in batch_examples]
      join_graph = pgl.graph.MultiGraph(graphs)
      labels = np.array(labels, dtype="int64").reshape(-1, 1)
      return join_graph, labels
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  from __future__ import absolute_import
  import os
  import sys
  import time
  import argparse
  import numpy
  import collections
  import paddle
  import paddle.fluid
  import paddle.fluid.layers
  import pgl
  from pgl.utils import mp_reader
  from pgl.utils.logger import log
label_desc: Use image node_id 2 for calling the GraphDataloader obj's underlying member method code with example usage: obj.batch_fn(batch_examples) and returns: join_graph,  labels