[Twisted-Python] Having some kind of "finally" clause

[Jean-Paul Calderone]

On Mon, 22 Sep 2008 15:12:53 +0200, Vincent Bernat <bernat at luffy.cx> wrote:
>
>Hi!
>
>I would like to do something like this with Twisted:
>
>x.open()
>try:
> x.someoperations()
> x.otheroperations()
>finally:
> x.close()
>
>I could do something like this :
>
>d = open_and_get_x()
>d.addCallback(someoperations)
>d.addCallback(otheroperations)
>d.addBoth(closeAndReRaiseIfError)
>return d
>
>Each callback would return x to let the next callback proceed it. However,
>if there is an error, I have no "x" to close in "closeAndReRaiseIfError".
>How can I do that?

There are a lot of ways.  You could make x an attribute of a shared object,
or you could close over it in the first callback to create the "finally"
handler, or you could pass it along as an argument to the `addBoth´ call
(again, in the first callback).

Notice that there's a slight difference between the two code examples you
gave.  The first won't close x in response to errors from `x.open()´, but
`closeAndReRaiseIfError´ will be called even for errors from `open_and_get_x´.
If you only add the finally handler in the first callback attached to `d´,
then this difference goes away.

Jean-Paul



>
>Thanks.
>
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