[Python-Dev] Third and hopefully final post: PEP 557, Data Classes

[Antoine Pitrou]

Or, simply, is_dataclass_instance(), which is even longer, but far more
readable thanks to explicit word boundaries :-)


On Thu, 30 Nov 2017 10:16:58 +0100
Antoine Pitrou <solipsis at pitrou.net> wrote:
> isdataclass() testing for instance-ship does sound like a bug magnet to
> me.
> 
> If isdataclassinstance() is too long (that's understandable), how about
> isdatainstance()?
> 
> Regards
> 
> Antoine.
> 
> 
> On Wed, 29 Nov 2017 17:02:21 -0800
> Guido van Rossum <guido at python.org> wrote:
> >  On Wed, Nov 29, 2017 at 3:51 PM, Carl Meyer <carl at oddbird.net> wrote:
> >   
> > > On 11/29/2017 03:26 PM, Eric V. Smith wrote:    
> > > > I've posted a new version of PEP 557, it should soon be available at
> > > > https://www.python.org/dev/peps/pep-0557/.
> > > >
> > > > The only significant changes since the last version are:
> > > >
> > > > - changing the "compare" parameter to be "order", since that more
> > > > accurately reflects what it does.
> > > > - Having the combination of "eq=False" and "order=True" raise an
> > > > exception instead of silently changing eq to True.
> > > >
> > > > There were no other issues raised with the previous version of the PEP.    
> > >
> > > Not quite; I also raised the issue of isdataclass(ADataClass) returning
> > > False. I still think that's likely to be a cause of bug reports if left
> > > as-is.
> > >    
> > 
> > I tried to look up the discussion but didn't find much except that you
> > flagged this as an issue. To repeat, your concern is that isdataclass()
> > applies to *instances*, not classes, which is how Eric has designed it, but
> > you worry that either through the name or just because people don't read
> > the docs it will be confusing. What do you suppose we do? I think making it
> > work for classes as well as for instances would cause another category of
> > bugs (confusion between cases where a class is needed vs. an instance
> > abound in other situations -- we don't want to add to that). Maybe it
> > should raise TypeError when passed a class (unless its metaclass is a
> > dataclass)? Maybe it should be renamed to isdataclassinstance()? That's a
> > mouthful, but I don't know how common the need to call this is, and people
> > who call it a lot can define their own shorter alias.
> >   
> 
> 
>