code: def PSRK_groups(self):
          r'''Dictionary of PSRK subgroup: count groups for the PSRK subgroups,
          as determined by `DDBST's online service <http://www.ddbst.com/unifacga.html>`_.
  
          Examples
          --------
          >>> pprint(Chemical('Cumene').PSRK_groups)
          {1: 2, 9: 5, 13: 1}
          '''
          if self.__PSRK_groups:
              return self.__PSRK_groups
          else:
              load_group_assignments_DDBST()
              if self.InChI_Key in DDBST_PSRK_assignments:
                  self.__PSRK_groups = DDBST_PSRK_assignments[self.InChI_Key]
                  return self.__PSRK_groups
              else:
                  return Nonf PSRK_groups(self):
          r'''Dictionary of PSRK subgroup: count groups for the PSRK subgroups,
          as determined by `DDBST's online service <http://www.ddbst.com/unifacga.html>`_.
  
          Examples
          --------
          >>> pprint(Chemical('Cumene').PSRK_groups)
          {1: 2, 9: 5, 13: 1}
          '''
          if self.__PSRK_groups:
              return self.__PSRK_groups
          else:
              load_group_assignments_DDBST()
              if self.InChI_Key in DDBST_PSRK_assignments:
                  self.__PSRK_groups = DDBST_PSRK_assignments[self.InChI_Key]
                  return self.__PSRK_groups
              else:
                  return None
docs: r'''Dictionary of PSRK subgroup: count groups for the PSRK subgroups,
          as determined by `DDBST's online service <http://www.ddbst.com/unifacga.html>`_.
  
          Examples
          --------
          >>> pprint(Chemical('Cumene').PSRK_groups)
          {1: 2, 9: 5, 13: 1}