[Twisted-Python] Understanding deferred and error handling

[Jason Rennie]

On Wed, Apr 20, 2011 at 12:28 AM, David <david at silveregg.co.jp> wrote:

>     def _stop(arg):
>         reactor.stop()
>     d.addBoth(_stop)
>

Try using addCallbacks instead of addBoth.  Then, you can logically separate
code to handle/print errors from "normal" code.

This will simply print no error in the log:
>

That's because you discarded the twisted.python.failure.Failure object by
using _stop for your errback and not doing anything with the arg.  Similar
to try/except with a "pass" in the "except" clause.

    def log_error(failure):

        log.err(failure.printTraceback())
>         return failure
>     d.addErrback(log_error)
>     d.addBoth(_stop)
>

Use d.addCallbacks(_stop, log_error) instead of addBoth/addErrback.  Also,
you probably want "log.err(failure.getTraceback())" instead of
"log.err(failure.printTraceback())".  printTraceback does not return a
meaningful value IIUC.

I don't get any traceback either.
>

Your traceback went to stdout whereas you were probably watching stderr or a
log file.

Jason

-- 
Jason Rennie
Research Scientist, ITA Software
617-714-2645
http://www.itasoftware.com/
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