[Twisted-Python] If the errbacks of a canceled Deferred are called with error other than CancelledError, is this acceptable?

Christopher Armstrong radix at twistedmatrix.com
Tue Jun 18 09:42:50 MDT 2013

On Tue, Jun 18, 2013 at 8:37 AM, Itamar Turner-Trauring <
itamar at futurefoundries.com> wrote:

> By way of background, Kai Zhang is one of our GSoC interns, working on
> adding Deferred cancellation support to Twisted. I believe the specific
> module he is working on is the POP3 client, but it's a general question -
> should we try to keep CancelledError percolating all the way to the top of
> callback chain when possible? My first thought is "yes" since that's a more
> informative reason, but maybe someone else has a counter-argument

I definitely think the error should explain that cancellation occurred; I
can also imagine cases where you'd want to know the specifics of how that
cancellation occurred, or how far some operation got before the
cancellation was executed (especially if we're talking about mutating
operations). ConnectionDone definitely doesn't sound good.

Christopher Armstrong
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