class_docstr: Implementation of knowledge graph interface in pglke.
  
  Args:
      triplets (dict):
          Triplet data of knowledge graphs with keys 'train', 'valid' and 'test'.
      num_ents (int, optional):
          Number of entities in a knowledge graph.
          If not provided, it will be inferred from triplets.
      num_rels (int, optional):
          Number of relations in a knowledge graph.
          If not provided, it will be inferred from triplets.
      ent_feat (np.ndarray, optional):
          Entity features, which have consistent order with entity ids.
      rel_feat (np.ndarray, optional):
          Relation features, which have consistent order with relation ids.
docstr: Relation features (np.ndarray).
          
docstr_tok: ["Relation","features","(","np.ndarray",")","."]
code: def rel_feat(self):
      """Relation features (np.ndarray)."""
      return self._rel_feat
  
imports: import os
  import json
  from collections import defaultdict
  import numpy
label_desc: Use image node_id 10 for calling the TriGraph obj's underlying member method code with example usage: obj.rel_feat() and returns: self