Method _checkout

lib/sqlalchemy/pool/base.py:1265–1388

(
        cls,
        pool: Pool,
        threadconns: Optional[threading.local] = None,
        fairy: Optional[_ConnectionFairy] = None,
    )

    @classmethod
    def _checkout(
        cls,
        pool: Pool,
        threadconns: Optional[threading.local] = None,
        fairy: Optional[_ConnectionFairy] = None,
    ) -> _ConnectionFairy:
        if not fairy:
            fairy = _ConnectionRecord.checkout(pool)

            if threadconns is not None:
                threadconns.current = weakref.ref(fairy)

        assert (
            fairy._connection_record is not None
        ), "can't 'checkout' a detached connection fairy"
        assert (
            fairy.dbapi_connection is not None
        ), "can't 'checkout' an invalidated connection fairy"

        fairy._counter += 1
        if (
            not pool.dispatch.checkout and not pool._pre_ping
        ) or fairy._counter != 1:
            return fairy

        # Pool listeners can trigger a reconnection on checkout, as well
        # as the pre-pinger.
        # there are three attempts made here, but note that if the database
        # is not accessible from a connection standpoint, those won't proceed
        # here.

        attempts = 2

        while attempts > 0:
            connection_is_fresh = fairy._connection_record.fresh
            fairy._connection_record.fresh = False
            try:
                if pool._pre_ping:
                    if not connection_is_fresh:
                        if fairy._echo:
                            pool.logger.debug(
                                "Pool pre-ping on connection %s",
                                fairy.dbapi_connection,
                            )
                        result = pool._dialect._do_ping_w_event(
                            fairy.dbapi_connection
                        )
                        if not result:
                            if fairy._echo:
                                pool.logger.debug(
                                    "Pool pre-ping on connection %s failed, "
                                    "will invalidate pool",
                                    fairy.dbapi_connection,
                                )
                            raise exc.InvalidatePoolError()
                    elif fairy._echo:
                        pool.logger.debug(
                            "Connection %s is fresh, skipping pre-ping",