Python Final and @ final examples

five.py

from typing import Final, Sequence

ADMIN_IDS: Final[Sequence[int]] = [1, 5]
# ADMIN_IDS: Final[Sequence[int]] = (1, 5)
# ADMIN_IDS: Final[tuple[int, ...]] = (1, 5, 8)


def main() -> None:
    print(ADMIN_IDS)
    ADMIN_IDS.append(7)
    print(ADMIN_IDS)


if __name__ == "__main__":
    main()
    # ADMIN_IDS = [1, 2, 3, 4, 5, 6, 7, 8, 9]
    # main()

four.py

from typing import Final


# wrong!
def example(value: Final[int]) -> None:
    print(value)


def main() -> None:
    example(123)
    example("foobar")


if __name__ == "__main__":
    main()

one.py

from typing import Final

PI: Final = 3.14


def circumference(diameter: float) -> float:
    return diameter * PI


def main() -> None:
    print(circumference(3))
    print(circumference(5))


if __name__ == "__main__":
    main()
    PI = 3
    main()

pyproject.toml

[tool.mypy]
python_version = "3.12"
pretty = true
strict = true

requirements.txt

mypy==1.9.0
mypy-extensions==1.0.0
typing_extensions==4.11.0

seven.py

from abc import ABC, abstractmethod
from typing import final


class Car:
    pass


class SuperCarBase(ABC):

    @abstractmethod
    def race(self) -> None:
        raise NotImplementedError


@final
class SuperCar(SuperCarBase):
    def race(self) -> None:
        print("Wrooom")


# class SuperDuperCar(SuperCar):
#     pass


def main() -> None:
    # print(SuperDuperCar())
    # print(SuperDuperCar.mro())

    print(SuperCar())
    print(SuperCar.mro())


if __name__ == "__main__":
    main()

six.py

from typing import final


class BaseConfig:

    def __init__(self) -> None:
        self.debug = False
        self.foo = "bar"

    @final
    def as_dict(self) -> dict[str, str]:
        return vars(self)


class Config(BaseConfig):

    def as_dict_new(self) -> dict[str, str]:
        return vars(self) | {"version": "2.0"}


def main() -> None:
    bc = BaseConfig()
    print(bc.as_dict())
    c = Config()
    print(c.as_dict())
    print(c.as_dict_new())


if __name__ == "__main__":
    main()

three.py

from typing import Final


class Point:
    x: Final[int]
    y: Final[int]

    def __init__(self, x: int, y: int) -> None:
        self.x = x
        self.y = y


def main() -> None:
    p1 = Point(1, 5)
    print(p1.x, p1.y)
    p1.y = 7
    print(p1.x, p1.y)


if __name__ == "__main__":
    main()

two.py

from typing import Final


class ConnectionBase:
    address: str = "localhost"
    timeout: Final[int] = 30


class TCPConnection(ConnectionBase):
    address: str = "127.0.0.1"
    # timeout: int = 10


def main() -> None:
    print(ConnectionBase.timeout)
    print(TCPConnection.timeout)


if __name__ == "__main__":
    main()