unsorted-dunder-slots (RUF023)

Fix is sometimes available.

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

What it does

Checks for __slots__ definitions that are not ordered according to a natural sort.

Why is this bad?

Consistency is good. Use a common convention for this special variable to make your code more readable and idiomatic.

Example

class Dog:
    __slots__ = "name", "breed"

Use instead:

class Dog:
    __slots__ = "breed", "name"

Fix safety

This rule's fix is marked as unsafe whenever Ruff can detect that code elsewhere in the same file reads the __slots__ variable in some way. This is because the order of the items in __slots__ may have semantic significance if the __slots__ of a class is being iterated over, or being assigned to another value.

In the vast majority of other cases, this rule's fix is unlikely to cause breakage; as such, Ruff will otherwise mark this rule's fix as safe. However, note that (although it's rare) the value of __slots__ could still be read by code outside of the module in which the __slots__ definition occurs, in which case this rule's fix could theoretically cause breakage.

Additionally, note that for multiline __slots__ definitions that include comments on their own line, it can be hard to tell where the comments should be moved to when sorting the contents of __slots__. While this rule's fix will never delete a comment, it might sometimes move a comment to an unexpected location.