code: def make_complete_graph(num_vertices, backend="python"):
      """
      Constructs a complete graph.
  
      The pairing function is: ``k = v1 + v2 * (v2 - 1) // 2``
  
      :param int num_vertices: Number of vertices.
      :returns: a 2 x K grid of (vertex, vertex) pairs.
      """
      if backend == "python":
          return _make_complete_graph(num_vertices)
      elif backend == "cpp":
          return _get_cpp_module().make_complete_graph(num_vertices)
      else:
          raise ValueError("unknown backend: {}".format(repr(backend)))
  
imports: import itertools
  import math
  import torch
  from torch.distributions import constraints
  from torch.distributions.utils import lazy_property
  from pyro.distributions.torch_distribution import TorchDistribution
label_desc: Use image node_id 2 for calling a global function with example usage: make_complete_graph(num_vertices, backend) and returns: _make_complete_graph, _get_cpp_module