non-slot-assignment (PLE0237)

Derived from the Pylint linter.

What it does

Checks for assignments to attributes that are not defined in __slots__.

Why is this bad?

When using __slots__, only the specified attributes are allowed. Attempting to assign to an attribute that is not defined in __slots__ will result in an AttributeError at runtime.

Known problems

This rule can't detect __slots__ implementations in superclasses, and so limits its analysis to classes that inherit from (at most) object.

Example

class Student:
    __slots__ = ("name",)

    def __init__(self, name, surname):
        self.name = name
        self.surname = surname  # [assigning-non-slot]
        self.setup()

    def setup(self):
        pass

Use instead:

class Student:
    __slots__ = ("name", "surname")

    def __init__(self, name, surname):
        self.name = name
        self.surname = surname
        self.setup()

    def setup(self):
        pass