[Python-ideas] @Override decorator

Guido van Rossum guido at python.org
Tue Jul 19 00:04:18 EDT 2016

The same argument would apply against abstractmethod... I have definitely
wondered when looking over some code whether it was defining or overriding
a method. But requiring people to always decorate overrides seems hard,
unless we made it a property that can be enforced by a metaclass, maybe?

On Monday, July 18, 2016, Steven D'Aprano <steve at pearwood.info> wrote:

> On Mon, Jul 18, 2016 at 09:44:45AM -0700, Shrey Desai wrote:
> > Why I would think an override decorator might be useful:
> > For other people reading the code, it would be great to distinguish
> > between methods that are unique to a class and methods that are
> > inherited from a parent class. Not all methods inherited might be
> > overridden, so keeping track of which inherited methods are overridden
> > and which are not would be nice.
> I fail to see that this is a sufficiently great problem to require a
> decorator. Occasionally I've added a comment to a method "Overriding
> mixin" or "Overriding class XXX" for example, but mostly I don't even
> bother. It's either obvious or unimportant or both. And when I do find
> myself writing such a comment, that's a good sign that my class
> hierarchy is too hard to understand and needs to be refactored.
> > With the advent of static typing from mypy:
> > Having the decorator could corroborate the fact that the given method
> > overrides the parent method correctly (correct name + parameter list).
> There is no requirement that the subclass method uses the same parameter
> names, or even signature, as the superclass method.
> > When the parent class changes, such as the name or parameter list of
> > an abstract method, the children classes should be updated as well.
> > mypy could easily target the methods that need to be altered with the
> > correct method signature.
> > If you don’t have an override decorator and overrode a parent method,
> > then there could be some error complaining about this. This would be
> > extremely useful to prevent accidental errors.
> I don't see it being very useful. Perhaps for people who have learned
> bad habits from Java and write deep class hierarchies, but we shouldn't
> encourage such anti-patterns. If people wish to write their own
> @override decorator, they should go right ahead, but I don't think it
> belongs in the standard library.
> --
> Steve
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--Guido (mobile)
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