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[Python-ideas] Composition over Inheritance

Nick Coghlan ncoghlan at gmail.com
Mon Oct 30 00:01:48 EDT 2017 
On 29 October 2017 at 21:44, Soni L. <fakedme+py at gmail.com> wrote:

> ORMs use this kind of descriptor based composition management extensively
> in order to reliably model database foreign key relationships in a way
> that's mostly transparent to users of the ORM classes.
>
>
> And this is how you miss the whole point of being able to dynamically
> add/remove arbitrary components on objects you didn't create, at runtime.
>

You can already do that by adding new properties to classes
post-definition, or by changing __class__ to refer to a different type, or
by wrapping objects in transparent proxy types the way wrapt does.

We *allow* that kind of thing, because it's sometimes beneficial in order
to get two libraries to play nicely together at runtime without having to
patch one or the other. However, it's a last resort option that you use
when you've exhausted the other more maintainable alternatives, not
something we actually want to encourage.

Cheers,
Nick.

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