[Python-Dev] short-circuiting runtime errors/exceptions in python debugger.

Chris Jerdonek chris.jerdonek at gmail.com
Mon Oct 29 14:59:10 EDT 2018

A simpler feature that could possibly help him (assuming there isn't any
external state to deal with) would be the ability to save everything at a
certain point in time, and then resume it later. He could rig things up to
save the state e.g. after every hour: 1 hour, 2 hours, etc. Then if an
error occurs after 2.5 hours, he could at least start resuming after 2
hours. This could be viewed as a cheap form of a reverse debugger, because
a reverse debugger has to save the state at every point in time, not just
at a few select points.


On Mon, Oct 29, 2018 at 9:51 AM Armin Rigo <armin.rigo at gmail.com> wrote:

> Hi,
> On Sat, 27 Oct 2018 at 01:50, Steven D'Aprano <steve at pearwood.info> wrote:
> > [...]
> > > So I was wondering if it would be possible to keep that context around
> > > if you are in the debugger and rewind the execution point to before
> > > the statement was triggered.
> >
> > I think what you are looking for is a reverse debugger[1] also known as
> > a time-travel debugger.
> I think it's a bit different.  A reverse debugger is here to debug
> complex conditions in a (static) program.  What Ed is looking for is a
> way to catch easy failures, fix the obviously faulty line, and
> continue running the program.
> Of course I can't help but mention to Ed that this is precisely the
> kind of easy failures that are found by *testing* your code,
> particularly if that's code that only runs after hours of other code
> has executed.  *Never* trust yourself to write correct code if you
> don't know that it is correct after waiting for hours.
> But assuming that you really, really are allergic to tests, then what
> you're looking for reminds me of long-ago Python experiments with
> resumable exceptions and patching code at runtime.  Both topics are
> abandoned now.  Resumable exceptions was a cool hack of the
> interpreter that nobody really found a use for (AFAIR); patching code
> at runtime comes with a pile of messes---it only works in the simple
> cases, but there is no general solution for that.
> A bientôt,
> Armin.
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