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redundant-bool-literal (RUF038)

Preview (since 0.8.0) · Related issues · View source

Fix is sometimes available.

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

What it does

Checks for Literal[True, False] type annotations.

Why is this bad?

Literal[True, False] can be replaced with bool in type annotations, which has the same semantic meaning but is more concise and readable.

bool type has exactly two constant instances: True and False. Static type checkers such as mypy treat Literal[True, False] as equivalent to bool in a type annotation.

Example

from typing import Literal

x: Literal[True, False]
y: Literal[True, False, "hello", "world"]

Use instead:

from typing import Literal

x: bool
y: Literal["hello", "world"] | bool

Fix safety

The fix for this rule is marked as unsafe, as it may change the semantics of the code. Specifically:

  • Type checkers may not treat bool as equivalent when overloading boolean arguments with Literal[True] and Literal[False] (see, e.g., #14764 and #5421).
  • bool is not strictly equivalent to Literal[True, False], as bool is a subclass of int, and this rule may not apply if the type annotations are used in a numeric context.

Further, the Literal slice may contain trailing-line comments which the fix would remove.

References