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Date: Sat, 15 Nov 2014 12:48:44 +1100
Subject: Re: I love assert
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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On Sat, Nov 15, 2014 at 12:30 PM, Marko Rauhamaa <marko@pacujo.net> wrote:
> Chris Angelico <rosuav@gmail.com>:
>
>> On Sat, Nov 15, 2014 at 11:12 AM, Marko Rauhamaa <marko@pacujo.net> wrote:
>>> Most importantly, assertion failures are not supposed to be recovered
>>> from (within the program). Assertion failures can result in the loss
>>> of life and limb. They can result in database corruption. They can
>>> result in monetary losses. They can result in smoke coming out of the
>>> monitor.
>>
>> Or, in theory, AssertionError just prevented any of the above from
>> happening.
>
> I'd advice against catching AssertionError and trying to recover from it
> within the program. You could catch it, log it and reraise it, but since
> the failure modes could be completely unexpected (really, by
> definition), I would move fault-tolerance outside the failing process
> and try to restore a coherent reality from there.

I agree - never catch it. But you should be able to prevent database corruption:

conn = establish_database_connection()
try:
    do_stuff()
finally:
    conn.rollback()

The raising of AssertionError anywhere inside do_stuff() will prevent
craziness from getting to the database, because it aborts the
execution. (You know, the way a royal pardon does.)

ChrisA