[Python-Dev] PEP 557: Data Classes
python-dev at mgmiller.net
Thu Oct 12 04:20:30 EDT 2017
On 2017-10-12 00:36, Stéfane Fermigier wrote:
> "An object that is not defined by its attributes, but rather by a thread of
> continuity and its identity." (from
Not sure I follow all this, but Python objects do have identities once
instantiated. e.g. >>> id('')
> See also the more general Wikipedia definition "An entity is something that
> exists as itself, as a subject or as an object, actually or potentially,
> concretely or abstractly, physically or not."
> In the context of DDD, entities are usually opposed to value objects: "An object
> that contains attributes but has no conceptual identity. They should be treated
> as immutable.". (https://en.wikipedia.org/wiki/Domain-driven_design#Building_blocks)
> Attrs, and by extension the dataclass proposal (I guess), provide some support
> for both:
> - Providing support for quickly constructing immutable objects from a bag of
> attributes, and providing equality based on those attributes, it helps implement
> Value Objects (not sure much more is needed actually)
> - By supporting equality based on some "primary key", it will also help with
> maintaining the concept of "equality" in entities.
I don't believe either module particularly supports or restricts immutability?
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