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Date: Wed, 03 Jun 2015 19:12:05 +0100
From: MRAB <python@mrabarnett.plus.com>
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To: python-list@python.org
Subject: Re: Retrying to send message
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On 2015-06-03 17:15, Cecil Westerhof wrote:
> Op Wednesday 3 Jun 2015 15:29 CEST schreef Chris Angelico:
>
>> On Wed, Jun 3, 2015 at 10:27 PM, Cecil Westerhof <Cecil@decebal.nl> wrote:
>>> def send_message(account_id, message, max_tries,
>>> terminate_program): error_msg = 'Something went wrong with: ' +
>>> message not_send = True tries = 0 while not_send: try:
>>> Core().update_status(account_id, message) except
>>> libturpial.exceptions.ServiceOverCapacity: tries += 1 print('Tried
>>> to send it {0} times'.format(tries)) if tries >= max_tries:
>>> terminate_program(error_msg) time.sleep(60) except:
>>> terminate_program(error_msg) else: not_send = False
>>>
>>> Is this a reasonable way to implement this, or is another way
>>> better? Well, maybe the timeout should be a parameter also. ;-)
>>
>> I'd skip the not_send flag and do the logic thusly:
>>
>> while True:
>> try:
>> update_status as above
>> break
>> except ServiceOverCapacity:
>> as above
>
> Yes that is much better. I now made it:
>      def send_message(account_id, message, max_tries, give_error, wait_time = 60):
>          error_msg   = 'Something went wrong with: ' + message
>          tries       = 0
>          while True:
>              try:
>                  Core().update_status(account_id, message)
>                  break
>              except libturpial.exceptions.ServiceOverCapacity:
>                  tries += 1
>                  print('Tried to send it {0} times'.format(tries))
>                  if tries >= max_tries:
>                      give_error(error_msg)
>                      return
>                  time.sleep(wait_time)
>              except:
>                  give_error(error_msg)
>                  return
>
>> And I'd also skip the bare except clause. If you get any sort of
>> exception, whether it's a bug, a failure from libturpial, a network
>> error, or anything else, your code will just terminate with a bland
>> and useless message. Much better to simply let the exception bubble
>> up.
>
> I kept the except. I like to see the message that went wrong. ;-)
>
You're still swallowing unexpected exceptions.

If any exception apart from ServiceOverCapacity is raised, the bare
except will just call 'give_error' and then return.

If you try to interrupt the program (^C on Windows, ^D on Linux), that'll
also be ignored.

> Also, in my case give_error terminates the program, but it never hurts
> to make functionality generic, so I added return statements. Not
> break, because on error you should leave the function. Break would in
> this instance do the same, but I find this neater.
>
>
>>> Also the documentation of time.sleep says:
>>> The actual suspension time may be less than that requested because
>>> any caught signal will terminate the sleep() following execution
>>> of that signal’s catching routine.
>>>
>>> My program does not much else as sending the message. So I think it
>>> is not necessary to cover for this possibility. Are I assuming to
>>> much?
>>
>> I wouldn't worry too much about a signal cutting your sleep short;
>> it doesn't look to me as if "exactly sixty seconds" is all that
>> crucial here. If your program sleeps for 42.645 seconds and then
>> gets woken up by a signal, and you retry a bit sooner than you
>> otherwise would have, is it going to break anything? If not, just
>> ignore that possibility.
>
> Correct, so I did not assume to much. :-D
>
> Usually I check parameters. But I understood that is not the Python
> way. For example a wait_time of 1, or negative is not useful. Also a
> max_tries of 10 ** 12 would not be very useful. But I can put the
> burden of the problem on the caller of the function?
>