Deprecate method into a propery

deprecation_property.py

"""Deprecation Property.

Using the decorated function as a property `A().value` works as intended,
while calling it `A().value()` will show the warning with the provided message.

```python
class Test:
    @deprecation_property
    def b(self):
        return "b"
```

"""

from __future__ import annotations

import warnings
from typing import Any, TypeVar

T = TypeVar("T")


class deprecation_property(property):  # noqa: N801
    """Property decorator warns if the user is calling the decorated as a method."""

    def __get__(self, obj: T, obj_type: type[T] | None = None) -> Any:  # noqa: ANN401
        value: Any = super().__get__(obj, obj_type)
        _property = self

        class _Proxy(type(value)):
            def __call__(self) -> Any:  # noqa: ANN401
                name = _property.fget.__name__ if _property.fget else "unknown property"  # ty:ignore[unresolved-attribute]
                warnings.warn(
                    f"Calling '{name}' as method is deprecated."
                    " Use it as a property instead.",
                    DeprecationWarning,
                    stacklevel=2,
                )
                return value

        try:
            return _Proxy(value)
        except TypeError:
            return _Proxy(*value)

deprecation_property_with_msg.py

"""Deprecation Property.

Alternative version that supports a custom message.

Using the decorated function as a property `A().value` works as intended,
while calling it `A().value()` will show the warning with the provided message.

```python
class Test:
    @deprecation_property
    def b(self):
        return "b"
```

"""
from __future__ import annotations

import warnings
from typing import Any, TypeVar

T = TypeVar("T")
def deprecation_property(
    message: str, warning_type: type[Warning] = DeprecationWarning
) -> type[property]:
    class _Property(property):
        def __get__(self, obj: T, obj_type: type[T] | None = None) -> Any:  # noqa: ANN401
            value: Any = super().__get__(obj, obj_type)

            class _Proxy(type(value)):
                def __call__(self) -> Any:  # noqa: ANN401
                    warnings.warn(message, warning_type, stacklevel=2)
                    return value

            try:
                return _Proxy(value)
            except TypeError:
                return _Proxy(*value)

    return _Property

test_deprecation_property.py

class Test:
    def __init__(self) -> None:
        self.value = "b"

    @deprecation_property
    def b(self) -> str:
        return self.value

    @b.setter
    def b(self, v: str) -> None:
        self.value = v


def test_deprecated_property_works_as_property():
    t = Test()
    p = t.b
    assert t.b == "b"


def test_deprecated_property_works_as_method():
    t = Test()
    assert t.b() == "b"


def test_deprecated_property_calls_warning():
    t = Test()
    with pytest.deprecated_call():
        t.b()


def test_deprecated_property_still_setter():
    t = Test()
    assert t.b == "b"
    t.b = "c"
    assert t.b == "c"

test_deprecation_property_with_msg.py

class Test:
    def __init__(self) -> None:
        self.value = "b"

    @deprecation_property("`.b()` is deprecated use `.b` instead")
    def b(self) -> str:
        return self.value

    @b.setter
    def b(self, v: str) -> None:
        self.value = v


def test_deprecated_property_works_as_property():
    t = Test()
    p = t.b
    assert t.b == "b"


def test_deprecated_property_works_as_method():
    t = Test()
    assert t.b() == "b"


def test_deprecated_property_calls_warning():
    t = Test()
    with pytest.deprecated_call():
        t.b()


def test_deprecated_property_still_setter():
    t = Test()
    assert t.b == "b"
    t.b = "c"
    assert t.b == "c"