@call
    def query_one(self, *args, **kw):
        i = self.query(*args, **kw)
        vs = list(i)

        if not vs:
            return None
        if len(vs) is not 1:
            raise OperationalError("more than one result returned from query_one()")

        return vs[0]
dataset/ETHPy150Open dieseldev/diesel/diesel/protocols/pg.py/PostgreSQLClient.query_one/operator `!=` -> `is not`