`final` keyword equivalent for variables in Python?

Question

I couldn\'t find documentation on an equivalent of Java\'s final in Python, is there such a thing?

I\'m creating a snapshot of an object (used for restorati

Answer 1

Python indeed does not have a final type, it does have immutable types such as tuples but that is something else.

Some of the other Answers here make classes full of pseudo final variables and I prefer my class to only have a few Final types, so I suggest using an descriptor to create the final type:

from typing import TypeVar, Generic, Type

T = TypeVar('T')

class FinalProperty(Generic[T]):
    def __init__(self, value: T):
        self.__value = value
    def __get__(self, instance: Type, owner) -> T:
        return self.__value
    def __set__(self, instance: Type, value: T) -> None:
        raise ValueError("Final types can't be set")

If you use this class like so:

class SomeJob:
    FAILED = FinalProperty[str]("Failed")

Then you will not be able to set that variable in any instance of that class. Unfortunately as with the WriteOnceReadWhenever answer you can still set the class variable.

job = SomeJob()
job.FAILED = "Error, this will trigger the ValueError"
SomeJob.FAILED = "However this still works and breaks the protection afterwards"