Emulating Final classes in Python

Wed Jan 18 02:05:33 EST 2017

On Wednesday 18 January 2017 15:42, Ethan Furman wrote:
[...]
> Both those cases are good candidates for disallowing subclassing.

I've given a metaclass that disallows subclassing:
class MyClass(MyParent, metaclass=FinalMeta):
 ...
Ethan took that one step further by giving a class you inherit from to disallow 
subclassing:
class MyClass(MyParent, Final):
 ...
Could we solve this problem with a decorator?
@final
class MyClass(MyParent):
 ...
Without needing to add any special magic to MyParent or MyClass, apart from the 
decorator, can we make MyClass final? That would (in principle) allow us to 
make a subclass, and *then* set the class final so that no more subclasses 
could be made.
I thought that the decorator could simply set the class' metaclass:
def final(cls):
 if cls.__class__ is type:
 cls.__class__ = Meta
 return cls
 raise TypeErrror('Possible metaclass conflict')
but that's disallowed. Any ideas?
-- 
Steven
"Ever since I learned about confirmation bias, I've been seeing 
it everywhere." - Jon Ronson