Add decorator django.utils.functional.cached_classproperty

[Boris Krause]

Hello,

I propose new feature - decorator cached_classproperty.

Django has a lot of methods for caching, like cached_page and cached_property.
Сaching improves response times.

For me it was useful.
What do you think about it?

https://github.com/django/django/pull/13813

Thanks!:)

[Tom Forbes]

I’m slightly skeptical - a cached class property seems slightly iffy and could be achieved with just a @functools.cache’d classmethod instead? 

Is there a specific use case where a cached, class _property_ would be the best way? And perhaps we need to care about concurrent access here, more than with our other cache implementations.

However, this is a really small change, so maybe it’s OK.

Tom

On 30 Dec 2020, at 14:46, Boris Krause <mgbi...@gmail.com> wrote:

Hello,

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[Adam Johnson]

There's no need for such a decorator - a class-level cached property can already be achieved with @classproperty and @lru_cache:

In [1]: from functools import lru_cache

In [2]: from django.utils.functional import classproperty

In [3]: class Thing:
   ...:     @classproperty
   ...:     @lru_cache(maxsize=1)
   ...:     def coefficient(cls):
   ...:         return 3.14
   ...:

In [4]: Thing.coefficient
Out[4]: 3.14

That said if I saw this in code I'd normally move it out into a standalone @lru_cache function - I don't see the need for it to be in a class, ad the caching behaviour often hides a potentially-expensive first operatio.

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Adam