docs: def get_factors(self, node=None):
          """
          Returns the factors that have been added till now to the graph.
  
          If node is not None, it would return the factor corresponding to the
          given node.
  
          Examples
          --------
          >>> from pgmpy.models import FactorGraph
          >>> from pgmpy.factors.discrete import DiscreteFactor
          >>> G = FactorGraph()
          >>> G.add_nodes_from(['a', 'b', 'c'])
          >>> phi1 = DiscreteFactor(['a', 'b'], [2, 2], np.random.rand(4))
          >>> phi2 = DiscreteFactor(['b', 'c'], [2, 2], np.random.rand(4))
          >>> G.add_factors(phi1, phi2)
          >>> G.add_nodes_from([phi1, phi2])
          >>> G.add_edges_from([('a', phi1), ('b', phi1),
          ...                   ('b', phi2), ('c', phi2)])
          >>> G.get_factors()
          >>> G.get_factors(node=phi1)
          """
          if node is None:
              return self.factors
          else:
              factor_nodes = self.get_factor_nodes()
              if node not in factor_nodes:
                  raise ValueError('Factors are not associated with the '
                                   'corresponding node.')
              factors = list(filter(lambda x: set(x.scope()) == set(self.neighbors(node)),
                                    self.factors))
              return factors[0]