🔒 How to create static properties while retaining type information?

[pastel oxide]

From Python 3.9 to 3.11, you could combine @classmethod and @property. However, this is now deprecated.

I found this thread: https://stackoverflow.com/questions/1697501/staticmethod-with-property

Which outlines a few possible solutions.

For example this: https://stackoverflow.com/a/76453871/12834165

class staticproperty(property):
  def __get__(self, owner_self, owner_cls):         
    return self.fget()

class classproperty(property):
  def __get__(self, owner_self, owner_cls):
    return self.fget(owner_cls)

And these work fine. However, I've not been able to implement typing in a way which MyPy accepts.

I'll happily accept alternative solutions as well.

Any help much appreciated 🙂

[manic compass]

@pastel oxide

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[merry smelt]

do you still need help with the problem? or maybe you figured it out yourself

[pastel oxide]

No, I have not figured it out

[merry smelt]

for the static one:

import typing

class staticproperty[T]:
    def __init__(self, f: typing.Callable[[], T]) -> None:
        self.f = f
    def __get__(self, _, __) -> T:
        return self.f()

seems to work
the class one im thinking a bit

im not sure if its even possible to make a generic classproperty like that

[pastel oxide]

Hmm. This seems very close, though I'm still getting errors.

Mypy: Function is missing a return type annotation [no-untyped-def]
Mypy: Method must have at least one argument. Did you forget the "self" argument? [misc]

For this test code

from typing import Any, Callable, Generic, TypeVar

T = TypeVar('T')


class staticproperty(Generic[T]):
    def __init__(self, f: Callable[[], T]) -> None:
        self.f = f

    def __get__(self, _: Any, __: Any) -> T:
        return self.f()


class Bean:
    @staticproperty
    def get_bean():
        return 'bean'


print(Bean.get_bean)

print(Bean.get_bean + '2')

I dont need a classproperty if staticproperty works 😁

[merry smelt]

well you didnt typehint get_bean, -> str or -> Literal["bean"]

[pastel oxide]

Yeah 🤦
But this error still stands:

Mypy: Method must have at least one argument. Did you forget the "self" argument? [misc]```

[merry smelt]

hmh

[pastel oxide]

I dont get it with Pylance, only with mypy

[merry smelt]

why does it think its a method, that seems like a bug

[pastel oxide]

Yeah, I think you're right. I'll report it in their issue tracker

[merry smelt]

seems like its actually "correct" in this one, even though it works

probally need to do something like this, ugly as hell though

from typing import Callable

class staticproperty[T]:
    def __init__(self, f: Callable[[], T]) -> None:
        self.f = f
    def __get__(self, _, __) -> T:
        return self.f()
    
class classproperty[C, T]:
    def __init__(self, f: Callable[[type[C]], T]) -> None:
        self.f = f
    def __get__(self, _, cls: type[C]) -> T:
        return self.f(cls)

class Q:
    @staticproperty
    @staticmethod
    def f() -> int:
        return 42
    @classproperty
    @classmethod
    def g(cls) -> int:
        return 42

[pastel oxide]

This looks like it yeah. Very cool, thank you 😁

!solved

[manic compass]

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