There's a piece of information I couldn't find over several searches. Two questions:

1. is there a simple way to prevent setting new class attrs?
2. while trying with the following snippet, shouldn't setattr(Derived, "test1", 1) call the __setattr__ from Base?

class Base:
    def __setattr__(self, key, value):
        raise PermissionError('in base')
    
    def __init_subclass__(cls, *args, **kwargs):
        def _setattr_(inst, key, val):
            raise PermissionError('in derived')
        cls.__setattr__ = _setattr_
        
class Derived(Base):
    pass

setattr(Derived, "test1", 1)

Derived.__setattr__(Derived, "test2", 2)
Traceback (most recent call last):
.
.
.
PermissionError: in derived

Base.__setattr__(Derived, "test3", 3)
Traceback (most recent call last):
.
.
.
PermissionError: in base

CodePudding user response：

Not without a metaclass.

The __setattr__ method you define in a class only affects instances of that class (or instances of subclasses), but not subclasses or the class itself (this is true for most methods exlcuding stuff like __new__ and __init_subclass__).

setattr(cls, attr_name, value) calls cls.__class__.__setattr__(cls, attr_name, value), but Derived.__class__ == type, not Base