[Twisted-Python] DeferredList and errback

Glyph Lefkowitz glyph at twistedmatrix.com
Sat Jul 13 21:18:38 EDT 2002


On Sun, 14 Jul 2002 02:55:49 +1000, Andrew Bennetts <andrew-twisted at puzzling.org> wrote:
> DeferredList takes care of this nicely, so long as it works.

Rather than adding a whole new class to defer.py, maybe you could make the
other deferred's errback get called by the first one?

> I realise I'm probably too late to get this into 0.19.0, but I'm wondering
> what the right way to provide this is:
>   - new class in defer.py (what would it be called?),

"DeferOneOrMany", maybe?  Tough thing to name.  This is probably the right
approach, though; consider that there are cases where one error might be all
you need, or one success.  In those cases you don't want to get a list as your
callback, you just want to get the one value.

>   - change the behaviour of DeferredList to do what I want, or

Definitely not!!  There are plenty of cases where you need _all_ the operations
to complete regardless of their status of completion.

>   - add a flag to the current DeferredList so it can do either behaviour?

As I said above, the behavior is really different; the types of the signatures
for your callbacks will be different.  That says "different class" to me.

-- 
 |    <`'>    |  Glyph Lefkowitz: Traveling Sorcerer   |
 |   < _/ >   |  Lead Developer,  the Twisted project  |
 |  < ___/ >  |      http://www.twistedmatrix.com      |
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