misplaced-bare-raise (PLE0704)

Derived from the Pylint linter.

This rule is unstable and in preview. The --preview flag is required for use.

What it does

Checks for bare raise statements outside of exception handlers.

Why is this bad?

A bare raise statement without an exception object will re-raise the last exception that was active in the current scope, and is typically used within an exception handler to re-raise the caught exception.

If a bare raise is used outside of an exception handler, it will generate an error due to the lack of an active exception.

Note that a bare raise within a finally block will work in some cases (namely, when the exception is raised within the try block), but should be avoided as it can lead to confusing behavior.

Example

from typing import Any


def is_some(obj: Any) -> bool:
    if obj is None:
        raise

Use instead:

from typing import Any


def is_some(obj: Any) -> bool:
    if obj is None:
        raise ValueError("`obj` cannot be `None`")