[Python-Dev] Concerns about method overriding and subclassing with dataclasses

[Ethan Smith]

On Fri, Dec 29, 2017 at 11:37 AM, Ethan Furman <ethan at stoneleaf.us> wrote:

> On 12/29/2017 02:23 AM, Ethan Smith wrote:
>
> The first is that needing both a keyword and method is duplicative and
>> unnecessary. Eric agreed it was a hassle, but
>> felt it was justified considering someone may accidentally override a
>> dataclass method. I disagree with this point of
>> view as dataclasses are billed as providing automatic methods. Overriding
>> via method definition is very natural and
>> idiomatic. I don't really see how someone could accidentally override a
>> dataclass method if methods were not generated
>> by the dataclass decorator that are already defined in the class at
>> definition time.
>>
>
> Accidental or not, the decorator should not be replacing methods defined
> by the class.
>
> The second concern, which I came across more recently, is if I have a base
>> class, and dataclasses inherit from this base
>> class, inherited __repr__ & co are silently overridden by dataclass. This
>> is both unexpected, and also means I need to
>> pass a repr=False to each subclass' decorator to get correct behavior,
>> which somewhat defeats the utility of
>> subclassing. Im not as sure a whole lot can be done about this though.
>>
>
> It is possible to determine whether an existing __repr__ is from 'object'
> or not, and only provide one if that is the case.  I think that should be
> the default, with 'repr = True' for those cases where a new,
> auto-generated, __repr__ is desired.
>

The only other thing you'd want to handle is to cover inheriting from
another dataclass. e.g., if I have dataclass with attribute a, and subclass
it to add attribute b, I'd want both in the repr.

~>Ethan Smith

>
> --
> ~Ethan~
>
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