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main.py

from __future__ import annotations

from dataclasses import dataclass
from contextvars import ContextVar, copy_context

from typing import Generic, TypeVar, overload, reveal_type

T = TypeVar("T")

class CtxProperty(Generic[T]):
    var: ContextVar[T]

    def __init__(self, var: ContextVar[T]) -> None:
        reveal_type(var)
        self.var = var

    def __set_name__(self, owner, name):
        reveal_type(owner)
        reveal_type(name)
        assert name == self.var.name

    @overload
    def __get__(self, instance: None, owner) -> CtxProperty[T]: ...

    @overload
    def __get__(self, instance, owner) -> T: ...

    def __get__(self, instance, owner=None) -> T | CtxProperty[T]:
        print(f"get: {type(instance)=}, {owner=}, var={self.var}")
        if instance is None:
            return self
        return self.var.get()

    def __set__(self, instance, value: T) -> None:
        print(f"set: {type(instance)=}, var={self.var}, {value=}")
        self.var.set(value)

@dataclass
class _Context:
    foo: CtxProperty[int] = CtxProperty(ContextVar("foo"))
    bar: CtxProperty[str] = CtxProperty(ContextVar("bar"))

ctx = _Context(
    foo = 0,
    bar = "hello",
)

reveal_type(ctx.foo)
reveal_type(ctx.bar)

print(ctx)
print(dict(copy_context()))
ctx.foo = 42
ctx.bar = "hello"
print(ctx)
print(dict(copy_context()))