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How would you write a descriptor supporting attribute DELETION via __delete__, and what real use case does that enable?

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Answer

Implement __delete__(self, instance) to run custom logic when 'del instance.attr' is called — useful for cleanup actions (like closing a resource, invalidating a related cache, or resetting to a default) that should happen specifically when an attribute is explicitly removed rather than just reassigned.
class ManagedResource:
    def __set_name__(self, owner, name):
        self.name = f"_{name}"
    def __get__(self, instance, owner):
        return getattr(instance, self.name, None)
    def __set__(self, instance, value):
        setattr(instance, self.name, value)
    def __delete__(self, instance):
        resource = getattr(instance, self.name, None)
        if resource:
            resource.close()  # cleanup runs specifically on 'del'
        delattr(instance, self.name)
Real-world example Ensuring a resource (like a file handle stored on an object) is properly released when its attribute is explicitly deleted with 'del'.

Common follow-ups: How does this differ in behavior and trigger conditions from cleanup logic placed in a class's __del__ method instead?

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