[Zope] handling exceptions for external methods

[Andreas Jung]

--On 6. Juli 2007 14:55:47 -0700 David Bear <David.Bear at asu.edu> wrote:

> I've begun using external methods and am trying to better understand the
> context they run and and how to handle exceptions. I have concluded
> the following (and I don't recall reading some of these in any
> documentation) (please correct me if I'm wrong)
>
> 1 external methods run in the same interpreter as zope

right

>
> 2 external methods have access to a larger namespace and therefor more
> functionality

they have access to the *full* Python functionality

>
> 3 external methods inherit the same namespace available to scripts
> running inside zope

inherit? Using 'self' as first parameter give you access to the
current object (for acquisition).

>
> 4 external methods are not launched as forked or spawned child
> processes

right

>
> 5 external methods do not have access to stdin/stdout

There is no usecase for accessing stdin from external methods and you might
to use stdout only for debugging purposes only.

>
> 6 external methods must return only strings,

Nonsense. External methods can return anything.

>but they may be unicode
> string as long as they are valid xml string data

Nonsense. There is no contract in Zope telling some method
to return XML at all.

>
> Something that I don't understand is how to handle an exception. For
> example, if I have an external method that appends data to the end of
> a file, if there is an IOException how to I capture it and send a
> message back to zope with something informative?

You must raise an exception if your failure is supposed to perform
a ZODB abort operation. Otherwise catch the exception and return some 
friendly error message back.

-aj

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