Python 3.8+typingterm

typing.final

decorators and markers

The @final decorator: the class must not be subclassed and the method must not be overridden. Only a type checker enforces it, not the interpreter.

Syntax

@final
class Leaf: ...

Do not confuse it with Final: typing.Final annotates a variable (MAX: Final = 10, 'do not reassign'), while @final decorates a class or a method. At runtime subclassing a @final class succeeds silently; only mypy or pyright report it. Since 3.11 the decorator sets __final__ = True, but that is an ordinary class attribute that subclasses inherit too, so getattr(Sub, '__final__') is True for a subclass as well — check vars(cls) instead.

Examples

# Python 3.11+
from typing import final
@final
class Leaf:
    pass
class Other(Leaf):  # mypy: Cannot inherit from final class
    pass
print(Leaf.__final__, getattr(Other, '__final__', False))  # → True True — атрибут унаследован
print('__final__' in vars(Other))  # → False

from typing import final
class Base:
    @final
    def done(self) -> str:
        return 'base'
class Sub(Base):
    def done(self) -> str:  # mypy: Cannot override final attribute
        return 'sub'
print(Sub().done())  # → sub — интерпретатор не мешает

See also

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