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Thread: Can I map "raise XXX" to some custom python exceptions?

Can I map "raise XXX" to some custom python exceptions?

From
"W. Matthew Wilson"
Date:
Right now, I have some triggers that can raise integrity constraint violations.

And in python, I have code like this:

    try:
        cursor.execute("...")
    except dbconn.InternalError, ex:

I'm working on code that handles buying and selling physical goods.
It would be nice to have exceptions that are more relevant to that
stuff -- I mean I want exceptions like "this good is not in the
warehouse" or "this good isn't available during that window of time".

Is this possible?

How do I map database exceptions to interesting exception types in python?

Matt


--
W. Matthew Wilson
matt@tplus1.com
http://tplus1.com

Re: Can I map "raise XXX" to some custom python exceptions?

From
"W. Matthew Wilson"
Date:
On Sun, Jun 19, 2011 at 1:02 PM, Dan Halbert <halbert@halwitz.org> wrote:

> Is it that you don't just want to raise your own exceptions manually, e.g.:
>
>   try:
>        cursor.execute("...")
>    except dbconn.InternalError, ex:
>        if ... :
>            raise OutOfStockException(...)

Yeah, this is what I'm doing now.  But there's a good chance that
something is going to get mapped to the OutOfStockException when it is
really a completely different kind of exception, like maybe I forgot
to set a non-null column.

So, really, I want to be able raise specific exceptions within
postgresql, and then define how those are converted to python objects.

Maybe I need to verify that postgresql supports custom exceptions.

Matt


--
W. Matthew Wilson
matt@tplus1.com
http://tplus1.com

Re: Can I map "raise XXX" to some custom python exceptions?

From
Daniele Varrazzo
Date:
On Sun, Jun 19, 2011 at 6:45 PM, W. Matthew Wilson <matt@tplus1.com> wrote:

> So, really, I want to be able raise specific exceptions within
> postgresql, and then define how those are converted to python objects.

It is an interesting use case. I've recently written a Postgres-based
program where I've used a specific sqlcode for the exceptions. It
would be nice having a mapping errcode->python exception instead of
using a pattern of catching and re-throwing.

However I suspect it wouldn't be a complete solution: still with my
specific example in mind, half of the exceptions are raised from
PL/pgSQL functions or triggers, where I have control over the errcode.
But other errors are generated by database-handled integrity
violations, so I don't see a way to generate an uniform errcode
throughout all the applications.

-- Daniele