assigning-non-slot / E0237

Message emitted:

Assigning to attribute %r not defined in class slots

Description:

Used when assigning to an attribute not defined in the class slots.

Problematic code:

class Student:
    __slots__ = ("name",)

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

    def setup(self):
        pass

Correct code:

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

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

    def setup(self):
        pass

Created by the classes checker.