class_docstr: Indexing edges for fast graph queries
  Sorted edges and represent edges in compressed style like csc_matrix or csr_matrix.
  
      Args:
          u: A list of node id to be compressed.
          v: A list of node id that are connected with u.
          num_nodes: The exactive number of nodes.
      
docstr: Return the degree of nodes.
          
docstr_tok: ["Return","the","degree","of","nodes","."]
code: def degree(self):
      """Return the degree of nodes."""
      return self._degree
  
imports: import os
  import json
  import copy
  import numpy
  import paddle
  from paddle.framework import core
  from pgl.utils import op
  import pgl.graph_kernel
  from pgl.utils.helper import check_is_tensor, to_paddle_tensor
label_desc: Use image node_id 4 for calling the EdgeIndex obj's underlying member method code with example usage: obj.degree() and returns: self