code: def filterAcceptsRow(self, row, parentindex):
          
          if not super(ReftrackSortFilterModel, self).filterAcceptsRow(row, parentindex):
              return False
          if parentindex.isValid():
              m = parentindex.model()
          else:
              m = self.sourceModel()
  
          i = m.index(row, 18, parentindex)
          reftrack = i.data(REFTRACK_OBJECT_ROLE)
          if not reftrack:
              return True
          else:
              return self.filter_accept_reftrack(reftrack)
docs: Return True, if the filter accepts the given row of the parent
  
          :param row: the row to filter
          :type row: :class:`int`
          :param parentindex: the parent index
          :type parentindex: :class:`QtCore.QModelIndex`
          :returns: True, if the filter accepts the row
          :rtype: :class:`bool`
          :raises: None