ruff/docs/rules/dynamically-typed-expression.md

dynamically-typed-expression (ANN401)

Derived from the flake8-annotations linter.

What it does

Checks that an expression is annotated with a more specific type than Any.

Why is this bad?

Any is a special type indicating an unconstrained type. When an expression is annotated with type Any, type checkers will allow all operations on it.

It's better to be explicit about the type of an expression, and to use Any as an "escape hatch" only when it is really needed.

Example

def foo(x: Any):
    ...

Use instead:

def foo(x: int):
    ...

References

• PEP 484
• typing.Any
• Mypy: The Any type