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[Python-ideas] Fwd: Define a method or function attribute outside of a class with the dot operator

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On 10 February 2017 at 16:25, Steven D'Aprano <steve at pearwood.info> wrote:> On Sat, Feb 11, 2017 at 01:25:40AM +1100, Chris Angelico wrote:>>> For what it's worth, my answers would be:>>>> __name__ would be the textual representation of exactly what you typed>> between "def" and the open parenthesis. __qualname__ would be built>> the exact same way it currently is, based on that __name__.>> If I'm reading this right, you want this behaviour:>> class Spam:>     pass>> def Spam.func(self): pass>> assert 'Spam.func' not in Spam.__dict__> assert 'func' in Spam.__dict__>> assert Spam.func.__name__ == 'Spam.func'> assert Spam.func.__qualname__ == 'Spam.Spam.func'>> If that's the case, I can only ask... what advantage do you see from> this? Because I can see plenty of opportunity for confusion, and no> advantage.What I would personally hope to see from the proposal is that given:    class Spam:        pass    def Spam.func(self):        return __class__the effective runtime behaviour would be semantically identical to:    class Spam:        def func(self):            return __class__such that:  * __name__ is set based on the method name after the dot  * __qualname__ is set based on the __name__ of the given class  * __set_owner__ is called after any function decorators are applied  * zero-argument super() and other __class__ references work properlyfrom the injected methodPotentially, RuntimeError could be raised if the reference before thedot is not to a type instance.If it *doesn't* do that, then I'd be -1 on the proposal, since itdoesn't add enough expressiveness to the language to be worth theextra syntax. By contrast, if it *does* do it, then it makes classdefinitions more decomposable, by providing post-definition access toparts of the machinery that are currently only accessible during theprocess of defining the class.The use case would be to make it easier to inject descriptors whenwriting class decorators such that they behave essentially the same asthey do when defined in the class body:    def my_class_decorator(cls):        def cls.injected_method(self):            # Just write injected methods the same way you would in a class body            return __class__        return cls(Actually doing this may require elevating super and __class__ to truekeyword expressions, rather than the pseudo-keywords they are now)Cheers,Nick.-- Nick Coghlan   |ncoghlan at gmail.com   |   Brisbane, Australia

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