[Twisted-Python] CONNECTION_LOST not an integer (docstring error?)
exarkun at divmod.com
Wed Oct 1 17:44:33 EDT 2008
On Wed, 1 Oct 2008 15:24:05 -0600, Michael McNeil Forbes <mforbes at physics.ubc.ca> wrote:
>On Oct 1, 2008, at 12:04 PM, Jean-Paul Calderone wrote:
>>On Wed, 1 Oct 2008 12:00:29 -0600, Michael McNeil Forbes
>><mforbes at physics.ubc.ca> wrote:
>>>Several places in the documentation refer to the method writeSomeData ()
>>>returning a negative integer if the connection is lost. (In particular
>>>However, twisted.internet.main.CONNECTION_LOST is often returned which
>>>is not an integer.
>>Hardly anyone actually needs `writeSomeData`. It's mostly an
>>detail of a certain group of reactors.
>I have opened a ticket. A question then that is sure to expose my
>ignorance of twisted...
>Why does writeSomeData not simply raise CONNECTION_LOST as an exception?
>Checking return values is quite un-pythonic. Is there a deep reason for
The reason is probably that whoever wrote it thought that raising an
exception would be enough slower than returning a special value that
it would be worth doing something slightly unusual. Compared to
returning a value, raising an exception is expensive in CPython, but
I doubt there is any surviving benchmark which demonstrates that it
makes a difference here.
However, it's a very low-level API and since it isn't intended to be
used by application code, it doesn't seem like a very high priority
to make it less confusing.
>P.S. I came across this because I was trying to use twisted running in a
>thread to write data resulting from a long computation that I have not yet
>turned into a producer. The more conventional "write" method was failing
>if the socket backed up, and provided no simple way of determining if data
>was being dropped. My solution was to used writeSomeData, and then have
>the computation decide to throw out some of the data if it is being
>produced too rapidly, but I need to know how much has been sent so I can
>decide what to throw away...
This seems more interesting than the main point of your email. :) You
should probably just do the work to turn the computation into a producer.
* writeSomeData is low level and crufty, as you've discovered
* Not all reactors have this API, so your program will break based on
the reactor selected to run it
* producers give you all the same information
Since you mentioned threads, I'll also point out that Twisted APIs are not
safe to use from non-reactor threads without reactor.callFromThread. If
you aren't using callFromThread, that would explain bad behavior from the
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