docstr: Get the number of nodes in the graph.
docstr_tok: ["Get","the","number","of","nodes","in","the","graph","."]
code: def number_of_vertices(self):
      """
      Get the number of nodes in the graph.
      """
      if self.properties.node_count is None:
          if self.adjlist is not None:
              self.properties.node_count = len(self.adjlist.offsets) - 1
          elif self.transposedadjlist is not None:
              self.properties.node_count = (
                  len(self.transposedadjlist.offsets) - 1
              )
          elif self.edgelist is not None:
              self.properties.node_count = len(self.nodes())
          else:
              raise RuntimeError("Graph is Empty")
      return self.properties.node_count
  
imports: from cugraph.structure import graph_primtypes_wrapper
  from cugraph.structure.graph_primtypes_wrapper import Direction
  from cugraph.structure.symmetrize import symmetrize
  from cugraph.structure.number_map import NumberMap
  import cugraph.dask.common.mg_utils
  import cudf
  import dask_cudf
  import cugraph.dask.comms.comms
  import pandas
  import numpy
  import warnings
  from cugraph.dask.structure import replication
  from typing import Union, Dict
  from pylibcugraph import get_two_hop_neighbors, select_random_vertices
  from pylibcugraph import ResourceHandle, GraphProperties, SGGraph
label_desc: Use image node_id 19 for calling the simpleGraphImpl obj's underlying member method code with example usage: obj.number_of_vertices() and returns: self