[Python-ideas] Decorator to avoid a mistake

[Paul Moore]

On 26 November 2016 at 07:16, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 26 November 2016 at 13:26, Guido van Rossum <guido at python.org> wrote:
>> I think one reason why such proposals are unwelcome to experienced users may
>> be that when done right this is totally legitimate, and the requirement to
>> use an @override decorator is just making code more verbose with very little
>> benefit.
>
> It's also the case that if we're going to provide decorators to help
> with class definitions, there are more valuable things that we can do
> beyond merely warning about accidental method and attribute overrides.

This comment made me think about another potential issue with the
@override proposal. If overriding a method without using the decorator
were to produce a warning, how would that interact with custom class
decorators or metaclasses that inject methods into a class? Would they
have to take special care to detect and mark overrides?

While it's true that if a custom metaclass injects an unintended
override, that's just as much a problem as if the user explicitly
writes one, the problem arises for the end user of such a custom
metaclass, who will get an obscure warning about internals that they
probably don't know how to fix.

Nothing insurmountable, sure, but it does act as a reminder that a
change like this could have pretty wide reaching implications...

Paul