[Python-Dev] PEP 557: Data Classes

Ethan Furman ethan at stoneleaf.us
Fri Sep 8 15:01:01 EDT 2017

On 09/08/2017 11:38 AM, Steven D'Aprano wrote:
> On Fri, Sep 08, 2017 at 10:37:12AM -0700, Nick Coghlan wrote:
>>>    def __eq__(self, other):
>>>        if other.__class__ is self.__class__:
>>>            return (self.name, self.unit_price, self.quantity_on_hand) ==
>>> (other.name, other.unit_price, other.quantity_on_hand)
>>>        return NotImplemented
>> My one technical question about the PEP relates to the use of an exact
>> type check in the comparison methods, rather than "isinstance(other,
>> self.__class__)".
> I haven't read the whole PEP in close detail, but that method stood out
> for me too. Only, unlike Nick, I don't think I agree with the decision.
> I'm also not convinced that we should be adding ordered comparisons
> (__lt__ __gt__ etc) by default, if these DataClasses are considered
> more like structs/records than tuples. The closest existing equivalent
> to a struct in the std lib (apart from namedtuple) is, I think,
> SimpleNamespace, and they are unorderable.

I'll split the difference.  ;)

I agree with D'Aprano that an isinstance check should be used, but I disagree with him about the rich comparison methods 
-- please include them.  I think unordered should only be the default when order is impossible, extremely difficult, or 


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