Add cached_staticproperty

[zmievsa]

Resolves #1

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[Atry]

The following test failed

def test__cached_classproperty__super():
    class Superclass:
        @cached_classproperty
        def my_cached_classproperty(cls):
            return ("Superclass",)
        @classmethod
        def my_classmethod(cls):
            return ("Superclass",)

    class Subclass1(Superclass):
        @cached_classproperty
        def my_cached_classproperty(cls):
            return (
                *super().my_cached_classproperty,
                "Subclass1",
            )
        @classmethod
        def my_classmethod(cls):
            return (
                *super().my_classmethod(),
                "Subclass1",
            )

    class Subclass2(Superclass):
        @cached_classproperty
        def my_cached_classproperty(cls):
            return (
                *super().my_cached_classproperty,
                "Subclass2",
            )
        @classmethod
        def my_classmethod(cls):
            return (
                *super().my_classmethod(),
                "Subclass2",
            )

    class Finalclass(Subclass1, Subclass2):
        @cached_classproperty
        def my_cached_classproperty(cls):
            return (
                *super().my_cached_classproperty,
                "Finalclass",
            )
        @classmethod
        def my_classmethod(cls):
            return (
                *super().my_classmethod(),
                "Finalclass",
            )

    assert Superclass.my_cached_classproperty == Superclass.my_classmethod()
    assert Subclass1.my_cached_classproperty == Subclass1.my_classmethod()
    assert Finalclass.my_cached_classproperty == Finalclass.my_classmethod()
    assert Subclass2.my_cached_classproperty == Subclass2.my_classmethod()

poetry run pytest
======================================================================= test session starts =======================================================================

platform win32 -- Python 3.11.0, pytest-7.2.2, pluggy-1.0.0
rootdir: C:\Users\atry\github\cached_classproperty
plugins: cov-4.0.0
collected 9 items                                                                                                                                                   

tests\test_classproperty.py ........F                                                                                                                        [100%]

============================================================================ FAILURES ============================================================================= 
________________________________________________________________ test__cached_classproperty__super ________________________________________________________________ 

    def test__cached_classproperty__super():
        class Superclass:
            @cached_classproperty
            def my_cached_classproperty(cls):
                return ("Superclass",)
            @classmethod
            def my_classmethod(cls):
                return ("Superclass",)

        class Subclass1(Superclass):
            @cached_classproperty
            def my_cached_classproperty(cls):
                return (
                    *super().my_cached_classproperty,
                    "Subclass1",
                )
            @classmethod
            def my_classmethod(cls):
                return (
                    *super().my_classmethod(),
                    "Subclass1",
                )

        class Subclass2(Superclass):
            @cached_classproperty
            def my_cached_classproperty(cls):
                return (
                    *super().my_cached_classproperty,
                    "Subclass2",
                )
            @classmethod
            def my_classmethod(cls):
                return (
                    *super().my_classmethod(),
                    "Subclass2",
                )

        class Finalclass(Subclass1, Subclass2):
            @cached_classproperty
            def my_cached_classproperty(cls):
                return (
                    *super().my_cached_classproperty,
                    "Finalclass",
                )
            @classmethod
            def my_classmethod(cls):
                return (
                    *super().my_classmethod(),
                    "Finalclass",
                )

        assert Superclass.my_cached_classproperty == Superclass.my_classmethod()
        assert Subclass1.my_cached_classproperty == Subclass1.my_classmethod()
>       assert Finalclass.my_cached_classproperty == Finalclass.my_classmethod()
E       AssertionError: assert ('Superclass', 'Finalclass') == ('Superclass'... 'Finalclass')
E         At index 1 diff: 'Finalclass' != 'Subclass2'
E         Right contains 2 more items, first extra item: 'Subclass1'
E         Use -v to get more diff

tests\test_classproperty.py:207: AssertionError
===================================================================== short test summary info ===================================================================== 
FAILED tests/test_classproperty.py::test__cached_classproperty__super - AssertionError: assert ('Superclass', 'Finalclass') == ('Superclass'... 'Finalclass')       
=================================================================== 1 failed, 8 passed in 0.11s ===================================================================

See https://github.com/atry/cached_classproperty/tree/add-cached-staticproperty

[zmievsa]

@Atry this looks like quite a normal behavior for cached properties, don't you think so?

[Atry]

I think @cached_classproperty should return the same value as @classproperty when the function does not have any side effect.

[zmievsa]

I am afraid it doesn't make sense as it breaks the "we run this thing once for every instance" rule because here classes are instances and this behavior would allow us to run it multiple times for a single instance if it was inherited.

I've taken a look at your test: only one of the asserts doesn't pass. All others do.

Also, an implementation would probably be pretty complex. What would you suggest?

[Atry]

I agree the "we run this thing once for every instance" rule. However, in test__cached_classproperty__super, Subclass2.my_cached_classproperty was not executed when cls is Finalclass.

I think the problem is that the cache keys of Subclass2.my_cached_classproperty and Superclass.my_cached_classproperty are the same, therefore they interfere each other

[Atry]

I wonder if using f"{id(self)}.{attrname}" or f"{id(owner)}.{attrname}" as the cache key would help.

[zmievsa]

Okay, your logic makes sense. Please, help me research how this specific situation is handled in other languages (Not the implementation but the behavior) and if it is indeed similar -- let's fix it and merge the new logic.

[Atry]

What else do you want to research other than the cache key uniqueness?

[zmievsa]

The fact that cached classproperties will re-execute for each parent class if called from a child class using super or any similar mechanism. If you believe that it is the case, then I'm ready to add the changes and merge them.

[Atry]

The fact that cached classproperties will re-execute for each parent class if called from a child class using super or any similar mechanism.

The behavior is expected to me. The only issue is the cache key uniqueness when the cached properties in subclass and superclass have the same name.

[zmievsa]

I guess let's think about the implementation, then. I'll try to tackle it this week. If you have time to play with it -- feel free to, I'll do my best to do reviews quickly.

[Atry]

I created https://github.com/Ovsyanka83/cached_classproperty/pull/3 to fix bugs that I reported in this PR