docs: def bnode_id(self):
          """
          calculates the bnode id for the class
          """
          if self.subject.type != 'bnode':
              return self.subject
          rtn_list = []
          for prop in sorted(self):
              for value in sorted(self[prop]):
                  rtn_list.append("%s%s" % (prop, value))
          return sha1("".join(rtn_list).encode()).hexdigest()