def sitecol(self):
        """
        Read the site collection from .filename and cache it
        """
        if 'sitecol' in vars(self):
            return self.__dict__['sitecol']
        if self.filename is None or not os.path.exists(self.filename):
            # case of nofilter/None sitecol
            return
        with hdf5.File(self.filename, 'r') as h5:
            self.__dict__['sitecol'] = sc = h5.get('sitecol')
        return sc