def METHOD_NAME(self, typename):
    for t in self.all_types:
        attr_name_t = "data_"+t
        data_thistype = getattr(self,attr_name_t)
        if t==typename:
            assert data_thistype is not None, "For type %r, attribute %r should contain data but is None"%(typename, attr_name_t)
        else:
            assert data_thistype is None, "For type %r, attribtue %r should be None but contains %r"%(typename, attr_name_t, data_thistype)