[Python-Dev] Second post: PEP 557, Data Classes

[Nick Coghlan]

On 27 November 2017 at 15:04, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
> Nick Coghlan wrote:
>>
>> Perhaps the check could be:
>>
>>   (type(lhs) == type(rhs) or fields(lhs) == fields(rhs)) and all
>> (individual fields match)
>
>
> I think the types should *always* have to match, or at least
> one should be a subclass of the other. Consider:
>
> @dataclass
> class Point3d:
>     x: float
>     y: float
>     z: float
>
> @dataclass
> class Vector3d:
>     x: float
>     y: float
>     z: float
>
> Points and vectors are different things, and they should never
> compare equal, even if they have the same field names and values.

And I guess if folks actually want more permissive structure-based
matching, that's one of the features that collections.namedtuple
offers that data classes don't.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia