[rabbitmq-discuss] AMQP & Python Write-Up

Thu Jan 15 00:58:53 GMT 2009

Barry & Gordon,

Entry has been updated with the correct no_ack explanation. Regarding
the None return on "no message waiting" from basic_get(), I chose to
explain that in words, rather than trap it out in the code to maintain
clarity.

http://blogs.digitar.com/jjww/2009/01/rabbits-and-warrens/

Thank you very much for your help.

-J

On Wed, Jan 14, 2009 at 5:28 PM, Barry Pederson <bp at barryp.org> wrote:
> Gordon Sim wrote:
>>
>> Jason J. W. Williams wrote:
>>>
>>> I've written up a quick start on the basics of AMQP and using it in
>>> Python, that is the kind of document I wished I'd been able to find in
>>> one place: http://blogs.digitar.com/jjww/2009/01/rabbits-and-warrens/
>>>
>>> It's probably laced with errors, and I'd appreciate any
>>> feedback/corrections.
>>
>> Nice article!
>>
>> I am not that familiar with py-amqplib but the no_ack argument to
>> basic_consume/basic_get is defined in the AMQP spec to mean that the server
>> should not expect an ack and should discard the message on delivery. I.e.
>> its an unreliable mode of delivery[1] rather than a signal to the client
>> library to automatically acknowledge on receiving a message.
>
> I just read the article too, very nice.
>
> Gordon's right about the no_ack flag, this sentence:
>
>  If you set the no_ack argument to true, then py-amqplib will
>  automatically send the acknowledgement immediately for you.
>
> should probably instead say something like what Gordon mentions above - it's
> the broker that acts differently based on that flag, not the client library.
>
> The only other thing I noticed was this section:
>
> ----
> Now, there's two methods of getting messages out of the queue. The first is
> to call chan.basic_get() to pull the next message off the queue:
>
>   1. msg = chan.basic_get("po_box")
>   2. print msg.body()
>   3. chan.basic_ack(msg.delivery_tag)
> ----
>
> If there isn't a message waiting in the queue when line 1 executes, then msg
> is set to None and line 2 will die since None does not have a "body"
> attribute.  Also, body is not a function to call, it's just a string, so
> this would be more appropriate:
>
>    msg = chan.basic_get("po_box")
>    if msg is not None:
>        print msg.body
>        chan.basic_ack(msg.delivery_tag)
>
> ================
>
>        Barry
>
>
>