When using clear_mappers is executed , celery mappings also got cleared

celery_task.py

@task
def columns( table = "usuarios"):
        try:
                t = Table( table , metadata, autoload = True, autoload_with = engine)
                try:
                        clear_mappers() # this clean all previous mappers if any
                        mapper( Dummy, t )
                except:
                        traceback.print_exc()
                        return "error"

                result = ["Table {} ( {} recs)".format(table, session.query( Dummy ).count())]
                for x in metadata.tables[table].columns:
                        result.append("{:<40s} {}".format( x.name, x.type))
                return "\n".join(result)
        except:
                traceback.print_exc()
        return "error"