Pyright: typing.Final should be error when used class attribute updating except __init__ method

[simon-ritchie]

Describe the bug

According to PEP 591, typing.Final can use to class attribute updating only in __init__ method but Pyright not report error when used it in other places.

A final attribute declared in a class body without an initializer must be initialized in the __init__ method (except in stub files):
https://www.python.org/dev/peps/pep-0591/#semantics-and-examples

Expected behavior
Error message should be displayed when set class attribute except in __init__ method (including when skipped initialization).

Screenshots or Code

from typing import Final


class Cat:

    name: Final[str] = 'bella'  # This line should report error msg (skipped initialization).

    def __init__(self) -> None:
        pass

    def set_age(self, age) -> None:
        self.age: Final[int] = 10  # This line should also report error msg because the method is not `__init__`.

VS Code extension or command-line

I'm using VS Code extension.

• Pyright version: 1.1.41
• VS Code version: 1.45.1
• OS: Windows 10

p.s.

If Pyright will not be supported PEP 591, please close this issue (because of PEP 591 not listed on README).

[erictraut]

By my reading of PEP 591, the first of the two cases in your example should not generate an error message.

class Cat:
    name: Final[str] = 'bella'

This is an acceptable usage of Final, as it defines a class variable. There are examples in the PEP documentation that mirror this usage.

The second case that you flagged should generate an error. This was an omission when I initially implemented support for PEP 591.

Thanks for the bug report — and for pointing out that I didn't mention PEP 591 in the documentation. Pyright does support both the final decorator and the Final annotation described in PEP 591.

[erictraut]

This will be fixed in the next version of Pyright.

[simon-ritchie]

@erictraut
Thx for replying.

This is an acceptable usage of Final, as it defines a class variable. There are examples in the PEP documentation that mirror this usage.

Ah... that's right. I was misunderstood.

This will be fixed in the next version of Pyright.

Thanks for handling it!

[erictraut]

This is now addressed in Pyright 1.1.42, which was just published.

[simon-ritchie]

Thanks for the update to fix it!

[erictraut]

Thanks for writing the article on Pyright!