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redundant-numeric-union (PYI041)

Derived from the flake8-pyi linter.

Fix is sometimes available.

What it does

Checks for parameter annotations that contain redundant unions between builtin numeric types (e.g., int | float).

Why is this bad?

The typing specification states:

Python’s numeric types complex, float and int are not subtypes of each other, but to support common use cases, the type system contains a straightforward shortcut: when an argument is annotated as having type float, an argument of type int is acceptable; similar, for an argument annotated as having type complex, arguments of type float or int are acceptable.

As such, a union that includes both int and float is redundant in the specific context of a parameter annotation, as it is equivalent to a union that only includes float. For readability and clarity, unions should omit redundant elements.

Example

def foo(x: float | int | str) -> None: ...

Use instead:

def foo(x: float | str) -> None: ...

Fix safety

This rule's fix is marked as safe, unless the type annotation contains comments.

Note that while the fix may flatten nested unions into a single top-level union, the semantics of the annotation will remain unchanged.

References