docs: def set_distributions(self):
          """
          Set distributions in the network.
  
          Examples
          --------
          >>> from pgmpy.readwrite.XMLBeliefNetwork import XBNWriter
          >>> writer =XBNWriter()
          >>> writer.set_distributions()
          """
          distributions = etree.SubElement(self.bnmodel, 'DISTRIBUTIONS')
  
          cpds = self.model.get_cpds()
          cpds.sort(key=lambda x: x.variable)
          for cpd in cpds:
              cpd_values = cpd.values.ravel()
              var = cpd.variable
              dist = etree.SubElement(distributions, 'DIST', attrib={'TYPE': self.model.node[var]['TYPE']})
              etree.SubElement(dist, 'PRIVATE', attrib={'NAME': var})
              dpis = etree.SubElement(dist, 'DPIS')
              evidence = cpd.variables[:0:-1]
              if evidence:
                  condset = etree.SubElement(dist, 'CONDSET')
                  for condelem in sorted(evidence):
                      etree.SubElement(condset, 'CONDELEM', attrib={'NAME': condelem})
                  # TODO: Get Index value.
                  for val in range(0, len(cpd_values), 2):
                      etree.SubElement(dpis, "DPI", attrib={'INDEXES': ' '}).text = \
                          " " + str(cpd_values[val]) + " " + str(cpd_values[val+1]) + " "
              else:
                  etree.SubElement(dpis, "DPI").text = ' ' + ' '.join(map(str, cpd_values))