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Invalid Raise

crates/ty_python_semantic/resources/lint_docs/invalid-raise.md

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Checks for raise statements that raise non-exceptions or use invalid causes for their raised exceptions.

Why is this bad?

Only subclasses or instances of BaseException can be raised. For an exception's cause, the same rules apply, except that None is also permitted. Violating these rules results in a TypeError at runtime.

Examples

python
def something():
    raise NameError


def cause() -> None:
    pass


def f():
    try:
        something()
    except NameError:
        # error: "Cannot raise object of type `Literal["oops!"]`"
        # error: "Cannot use object of type `def cause() -> None` as an exception cause"
        raise "oops!" from cause


def g():
    # error: "Cannot raise `NotImplemented`"
    # error: "Cannot use object of type `Literal[42]` as an exception cause"
    raise NotImplemented from 42

Use instead:

python
def something():
    raise NameError


def f():
    try:
        something()
    except NameError as e:
        raise RuntimeError("oops!") from e


def g():
    raise NotImplementedError from None

References