How to use the lmdb.NotFoundError function in lmdb

def _from_existing_db(db, complevel=6):
    readonly = db.flags().get('readonly')

    try:
        db_info = db.open_db(b'info', create=False)
    except lmdb.NotFoundError:
        raise ValueError('Existing database is not a ds cache')

    with db.begin(db_info, write=False) as tr:
        version = tr.get(b'version', None)
        if version is None:
            raise ValueError('Missing format version field')
        if version != FORMAT_VERSION:
            raise ValueError("Unsupported on disk version: " + version.decode('utf8'))

        zdict = tr.get(b'zdict', None)

    dbs = SimpleNamespace(main=db,
                          info=db_info,
                          groups=db.open_db(b'groups', create=False),
                          ds=db.open_db(b'ds', create=False),
                          udata=db.open_db(b'udata', create=False))

try:
            self.set_binlog(enable=False)
            if binlog:
                self.set_binlog(enable=True)
                # try:
                #     self._semaphore = Semaphore(semaphore_path(name))
                # except ExistentialError:
                #     pass
                self._binlog = self._env.open_db(b'__binlog__', create=binlog)
                self._binidx = self._env.open_db(b'__binidx__', create=binlog)
                with self._env.begin(write=True) as txn:
                    if not txn.stat(db=self._binlog)['entries']:
                        dat = dumps({'txn': []}).encode()
                        txn.put(pack('>Q', 1), dat, db=self._binlog, append=False)

        except lmdb.NotFoundError:
            pass
        except:
            raise