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

Wes Turner wes.turner at gmail.com
Thu Nov 30 06:43:10 EST 2017

Sorry, this one shouldn't be "an"; " a" was correct::

repr: If true (the default), an __repr__ method will be generated.

Note that repr can be dangerous with user-supplied input because of terminal control character injection (e.g. broken syntax highlighting, \r, character set, LEDs,)

On Thursday, November 30, 2017, Wes Turner <wes.turner at gmail.com> wrote:

Could these be things in types?

types.ClassType types.InstanceType types.DataClass types.DataClassInstanceType (?) I sent a PR with typo fixes and .. code:: python directives so that syntax highlighting works (at least on GitHub). https://github.com/python/peps/blob/master/pep-0557.rst https://github.com/python/peps/pull/488 Additional notes: - "DataClass" instead of "Data Class" would be easier to search for. s/DataClass/Data Class/g? - It's probably worth mentioning how hash works when frozen=True also here: https://github.com/python/peps/blob/master/pep-0557.rst#frozen-instances - The hash explanation could be a two column table for easier readability What a great feature. - Runtime data validation from annotations (like PyContracts,) would be cool - slots are worth the time On Thursday, November 30, 2017, Antoine Pitrou <solipsis at pitrou.net_ _<javascript:e(%7B%7D,'cvml','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. >

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