[Python-Dev] Dataclasses and correct hashability

[Chris Barker]

On Fri, Feb 2, 2018 at 7:38 AM, Elvis Pranskevichus <elprans at gmail.com>
wrote:

> On Friday, February 2, 2018 10:08:43 AM EST Eric V. Smith wrote:
> > However, I don't feel very strongly about this. As I've said, I expect
> > the use cases for hash=True to be very, very rare.
>
> Why do you think that the requirement to make a dataclass hashable is a
> "very, very rare" requirement?


I think what's rare is wanting hashability without it being frozen.


> Just put yourself in the shoes of an average Python developer.  You try
> to put a dataclass in a set, you get a TypeError.  Your immediate
> reaction is to add "hash=True".  Things appear to work.


agreed, the easy and obvious way should be to make it frozen -- if it's
hard to make it hashable and not frozen, then that's good.

But it is nice to have the __hash__ generated more you.... so maybe a flag
for "unfrozen_hashable" -- really klunky, but if that is a rare need, then
there you go.

Or maybe:

If either hash or frozen is specified, it become both frozen and hashable.

If both are specified, then it does what the user is asking for.

-CHB
-- 

Christopher Barker, Ph.D.
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