How to retry something with a timeout in Python?

[tinnews at isbd.co.uk]

Scott David Daniels <Scott.Daniels at acm.org> wrote:
> tinnews at isbd.co.uk wrote:
> > This feels like it should be simple but I can't see a clean way of
> > doing it at the moment.
> > 
> > I want to retry locking a file for a number of times and then give up,
> > in pseudo-code it would be something like:-
> > 
> > 
> >     for N times
> >         try to lock file
> >             if successful break out of for loop
> >     if we don't have a lock then give up and exit
> 
>      for attempt in range(N):
>           try:
>               lock_file_with_timeout(per_try)  # change to what you mean
>           except LockAttemptFailure: # or however the failure is shown
>               pass  # here the attempt+1th try failed.
>           else:
>               break # success -- have the lock
>      else:
>          raise ImTiredError  # however you handle N attempts w/o success
>      <rest_of_code>
> 
Ah, yes, it's the 'else:' with the 'for' that makes it easier, I've
come from languages which don't have that, thank you!  :-)

> Often it is easiest to stick it in a function:
> 
>      def retry_lock(tries=3, wait_per_attempt=.5):
>          for attempt in range(tries):
>              try:
>                  # change following to whatever you do to attempt a lock.
>                  lock_file_with_timeout(wait_per_attempt)
>              except LockAttemptFailure: # or however the failure is shown
>                  pass  # here the attempt+1th try failed.
>              else:
>                  return # success -- have the lock
>          raise ImTiredError
> 
> --Scott David Daniels
> Scott.Daniels at Acm.Org

-- 
Chris Green