class_docstr: Implementation of multiple disjoint graph structure in pgl.
  
  This is a simple implementation of graph structure in pgl.
  
  Args:
      graph_list :  A list of Graph Instances
  
  Examples:
  
      .. code-block:: python
      
          batch_graph = MultiGraph([graph1, graph2, graph3])
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code: def __init__(self, graph_list):
      num_nodes = np.sum([g.num_nodes for g in graph_list])
      node_feat = self._join_node_feature(graph_list)
      edge_feat = self._join_edge_feature(graph_list)
      edges = self._join_edges(graph_list)
      super(MultiGraph, self).__init__(
          num_nodes=num_nodes,
          edges=edges,
          node_feat=node_feat,
          edge_feat=edge_feat,
      )
      self._num_graph = len(graph_list)
      self._src_graph = graph_list
      graph_lod = [g.num_nodes for g in graph_list]
      graph_lod = np.cumsum(graph_lod, dtype="int32")
      graph_lod = np.insert(graph_lod, 0, 0)
      self._graph_lod = graph_lod
  
imports: import os
  import numpy
  import pickle
  import time
  import pgl.graph_kernel
  from collections import defaultdict
label_desc: Use image node_id 1 to create a new MultiGraph object from inherited base classes: Graph with example: obj = MultiGraph(graph_list)