On Thu, Mar 29, 2012 at 6:59 PM, Chris McDonough <chr...@plope.com> wrote:
> On Thu, 2012-03-29 at 07:18 -0400, Jim Fulton wrote:
>> On Wed, Mar 28, 2012 at 6:37 PM, Chris McDonough <chr...@plope.com> wrote:
>> > On Wed, 2012-03-28 at 17:06 -0400, Jim Fulton wrote:
>> >> On Wed, Mar 28, 2012 at 4:37 PM, Chris McDonough <chr...@plope.com> wrote:
>> >> > On Wed, 2012-03-28 at 14:21 -0400, Jim Fulton wrote:
>> >> ...
>> >> > A decorator for running some code in the context of a txn and retrying
>> >> > retryable exceptions would be nice higher level behavior. Â I'd be
>> >> > willing to do this work over this weekend.
>> >>
>> >> Cool. Don't forget the transaction note part. :)
>> >> Too many transactions in our apps don't have
>> >> notes, especially transactions that happen
>> >> outside of web requests.
>> >>
>> >> > In the meantime, I think the existing attempts context manager still
>> >> > needs the small fix I proposed in my original message. Â Can you confirm
>> >> > that my understanding of the its intent seems roughly correct?
>> >>
>> >> I didn't see a statement of intent. I think your fix us good,
>> >> but the code (that I wrote and your fix) makes my head hurt. :)
>> >>
>> >> I'd say, make some test cases for the bug and make it pass.
>> >
>> > OK. Once I fix this "Attempts" bug, I think the decorator code is just
>> > a higher level interface that uses it:
>> >
>> > class job(object):
>> > def __init__(self, attempts=1, note=None, manager=None):
>> > self.attempts = attempts
>> > self.note = note
>> > if manager is None:
>> > manager = transaction.manager
>> > self.manager = manager
>> >
>> > def __call__(self, wrapped):
>> > note = self.note
>> > if note is None:
>> > note = getattr(wrapped, '__name__', None)
>> > def inner(*arg, **kw):
>> > for attempt in self.manager.attempts(self.attempts):
>> > with attempt as t:
>> > t.note(note)
>> > return wrapped(*arg, **kw)
>> >
>> > .. or something like that...
>>
>> It could be written that way, although I would
>> use a much simpler implementation.
>>
>> The attempt design was a reach to overcome
>> the limitations of the with statement. I'm not at all happy
>> with it, although I couldn't think of anything better at the
>> time. I hate to build on it.
>
> It's brainbusting, yes, but it works. Do you have any other specific
> pattern in mind?
def job(func=None, retries=3):
if func is None:
return lambda f: job(f, retries)
note = func.__doc__
if note:
note = note.split('\n', 1)[0]
else:
note = func.__name__
for i in xrange(retries + 1):
t = manager.begin()
if i:
t.note("%s (retry: %s)" % (note, i))
else:
t.note(note)
try:
func(t)
t.commit()
except TransientError:
t.abort()
else:
break
The above is untested, but you get the idea.
Aside from note and decorator support,
this is straightforward. It encapsulates
standard boilerplate.
Jim
--
Jim Fulton
http://www.linkedin.com/in/jimfulton
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