class_docstr: FB15k237 link prediction dataset.
  
  FB15k-237 is a subset of FB15k where inverse
  relations are removed. When creating the dataset,
  a reverse edge with reversed relation types are
  created for each edge by default.
  
  FB15k237 dataset statistics:
  
  - Nodes: 14541
  - Number of relation types: 237
  - Number of reversed relation types: 237
  - Label Split:
  
      - Train: 272115
      - Valid: 17535
      - Test: 20466
  
  Parameters
  ----------
  reverse : bool
      Whether to add reverse edge. Default True.
  raw_dir : str
      Raw file directory to download/contains the input data directory.
      Default: ~/.dgl/
  force_reload : bool
      Whether to reload the dataset. Default: False
  verbose : bool
      Whether to print out progress information. Default: True.
  transform : callable, optional
      A transform that takes in a :class:`~dgl.DGLGraph` object and returns
      a transformed version. The :class:`~dgl.DGLGraph` object will be
      transformed before every access.
  
  Attributes
  ----------
  num_nodes: int
      Number of nodes
  num_rels: int
      Number of relation types
  
  Examples
  ----------
  >>> dataset = FB15k237Dataset()
  >>> g = dataset.graph
  >>> e_type = g.edata['e_type']
  >>>
  >>> # get data split
  >>> train_mask = g.edata['train_mask']
  >>> val_mask = g.edata['val_mask']
  >>> test_mask = g.edata['test_mask']
  >>>
  >>> train_set = th.arange(g.num_edges())[train_mask]
  >>> val_set = th.arange(g.num_edges())[val_mask]
  >>>
  >>> # build train_g
  >>> train_edges = train_set
  >>> train_g = g.edge_subgraph(train_edges,
                                relabel_nodes=False)
  >>> train_g.edata['e_type'] = e_type[train_edges];
  >>>
  >>> # build val_g
  >>> val_edges = th.cat([train_edges, val_edges])
  >>> val_g = g.edge_subgraph(val_edges,
                              relabel_nodes=False)
  >>> val_g.edata['e_type'] = e_type[val_edges];
  >>>
  >>> # Train, Validation and Test
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docstr: The number of graphs in the dataset.
docstr_tok: ["The","number","of","graphs","in","the","dataset","."]
code: def __len__(self):
      r"""The number of graphs in the dataset."""
      return super(FB15k237Dataset, self).__len__()
  
imports: from __future__ import absolute_import
  import os, sys
  import pickle
  import networkx
  import numpy
  import scipy.sparse
  from ..None import backend
  from ..convert import graph
  from ..utils import retry_method_with_fix
  from .dgl_dataset import DGLBuiltinDataset
  from .utils import _get_dgl_url, deprecate_function, deprecate_property, download, extract_archive, generate_mask_tensor, get_download_dir, load_graphs, load_info, makedirs, save_graphs, save_info
label_desc: Use image node_id 3 for calling the FB15k237Dataset obj's underlying member method code with example usage: obj.__len__() and returns: super