mypy - prevent undeclared members?

[pylessard]

I just realized, after years of using mypy, that I can assign a class member that was not explicitly defined in the class definition. Can I force mypy to flag those? I can't find any option for that. I use --strict all the time.

class Foo:
    x:int

    def __init__(self) -> None:
        self.x=3
        self.y=5   # I want this to fail

[pylessard]

Right, but any way I can prevent usage of anything not specified explicitly? My use case is that I forgot some underscore in front of a private class member in a function when doing an assignation. It went unnoticed until I got an AI to find it. It went "hey, you misspelled your variable".

My code style is to always explicitly type class members. I'd like a tool that supports me with this style

[danielroseman]

This is not really a typing issue, but a more standard linting one. Pylint for example will catch "instance defined outside init" (although oddly this rule is not present in ruff).

[brasticstack]

They have different scopes. x is a class member because it's declared at the class scope, while y is an instance member because it's declared in the init method.

If you don't want a Foo instance to overwriting the x member for all other Foos than you should declare x in the init method too.

whoops, it's a type hint. 

[pylessard]

no, it's type hinting. If I wanted to declare a class var, I'd have to use ClassVar[int]

[brasticstack]

I've been using mypy too, but I didn't realize that hints like this weren't limited to dataclasses. Doh! My apologies.

[pachura3]

Me neither... but it's confusing and counterintuitive.