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missing-return-type-special-method (ANN204)#

Derived from the flake8-annotations linter.

Fix is sometimes available.

What it does#

Checks that "special" methods, like __init__, __new__, and __call__, have return type annotations.

Why is this bad?#

Type annotations are a good way to document the return types of functions. They also help catch bugs, when used alongside a type checker, by ensuring that the types of any returned values, and the types expected by callers, match expectation.

Note that type checkers often allow you to omit the return type annotation for __init__ methods, as long as at least one argument has a type annotation. To opt-in to this behavior, use the mypy-init-return setting in your pyproject.toml or ruff.toml file:

mypy-init-return = true


class Foo:
    def __init__(self, x: int):
        self.x = x

Use instead:

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