[Python-Dev] PEP 553

[Yarko Tymciurak]

On Wed, Oct 4, 2017 at 7:50 PM, Barry Warsaw <barry at python.org> wrote:

> On Oct 4, 2017, at 20:22, Yarko Tymciurak <yarkot1 at gmail.com> wrote:
>
> > I've recently started using a simple conditional breakpoint in ipython,
> and wonder if  - in addition to Nick Coghlan's request for the env
> 'PYTHONBREAKPOINT'  (boolean?), it would make sense (I _think_ so) to add a
> condition parameter to the breakpoint() call.  This does raise several
> questions, but it seems that it could make for a simple unified way to
> conditionally call an arbitrary debugger.  What I found useful (in the
> contecxt of ipython - but general enough) you can see in this gist:
> https://gist.github.com/yarko/bdaa9d3178a6db03e160fdbabb3a9885
> >
> > If PEP 553's breakpoint() were to follow this sort of interface (with
> "condition"), it raises a couple of questions:
> > - how would a missing (default) parameter be done?
> > - how would parameters to be passed to the debugger "of record" be
> passed in (named tuple? - sort of ugly)
> > - would PYTHONBREAKPOINT be a global switch (I think yes), vs a
> `condition` default.
> >
> > I have no dog in the fight, but to raise the possibility (?) of having
> PEP 553 implement simple conditional breakpoint processing.
>
> Thanks for bringing this up Yarko.  I think this could be done with the
> current specification for PEP 553 and an additional API from the various
> debuggers.  I don’t think it needs to be part of PEP 553 explicitly, given
> the additional complications you describe above.
>
> Remember that both built-in breakpoint() and sys.breakpointhook() accept
> *args, **kws, and it is left up to the actual debugger API to
> interpret/accept those additional arguments.  So let’s say you wanted to
> implement this behavior with pdb.  I think you could do something as simple
> as:
>
> def conditional_set_trace(*, condition=True):
>     if condition:
>         pdb.set_trace()
>
> sys.breakpointhook = conditional_set_trace
>
> Then in your code, you would just write:
>
> def foo(value):
>     breakpoint(condition=(value < 0))
>
> With the IPython gist you referenced, you wouldn’t even need that
> convenience function.  Just set sys.breakpointhook=conditional_breakpoint.breakpoint_
> and viola!
>
> You could also PYTHONBREAKPOINT=conditional_breakpoint.breakpoint_
> python3.7 … and it should Just Work.
>

Thanks Barry - yes, I see:  you're correct.   Thanks for the pep!
- Yarko


>
> Cheers,
> -Barry
>
>
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