delegation pattern via descriptor
in [Python]
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From: kedra marbun on 2 Jul 2010 09:28 hello, friendliest prog lang community on earth ;) i'm feeling that (0) delegation pattern thru descriptor encourages dedicated delegate for each task, if feeling: print(benefits) (1) the delegate is designed to be blind about the class on which the delegate is attached to isn't that the two strengthen the coupling between delegator & delegate obviously __getattribute__ & his 2 friends of 'object' & 'type' have what it takes to make it not like that, it's just that they're not designed to pass it. thus i think it is by design yes i know there's a way around it, the most obvious to me is defining your own hooks (which is not trival, at least to me) , but like i said, it's encouraged wow, it's almost time for brazil to beat the dutch, sorry Guido ;) if fifa['wc']['2010'].winner is not brazil: raise SystemError
From: Steven D'Aprano on 2 Jul 2010 11:35 On Fri, 02 Jul 2010 06:28:59 -0700, kedra marbun wrote: > hello, friendliest prog lang community on earth ;) > > i'm feeling that > (0) delegation pattern thru descriptor encourages dedicated delegate for > each task, if feeling: print(benefits) (1) the delegate is designed to > be blind about the class on which the delegate is attached to > > isn't that the two strengthen the coupling between delegator & delegate > obviously __getattribute__ & his 2 friends of 'object' & 'type' have > what it takes to make it not like that, it's just that they're not > designed to pass it. thus i think it is by design > > yes i know there's a way around it, the most obvious to me is defining > your own hooks (which is not trival, at least to me) , but like i said, > it's encouraged I'm sorry, I don't understand a thing you're saying there. Can you explain what you mean? -- Steven
From: Mark Lawrence on 3 Jul 2010 05:08 On 02/07/2010 14:28, kedra marbun wrote: > hello, friendliest prog lang community on earth ;) Flattery will get you everywhere. > [snip] > > wow, it's almost time for brazil to beat the dutch, sorry Guido ;) > if fifa['wc']['2010'].winner is not brazil: raise SystemError Have you run this and get your SystemError yet? :) Kindest regards. Mark Lawrence
From: Bruno Desthuilliers on 3 Jul 2010 05:15 kedra marbun a �crit : > if we limit our discussion to py: > why __{get|set|delete}__ don't receive the 'name' & 'class' from > __{getattribute|{set|del}attr}__ > 'name' is the name that is searched While it would have been technically possible, I fail to imagine any use case for this.
From: Gregory Ewing on 3 Jul 2010 22:50
Bruno Desthuilliers wrote: > kedra marbun a écrit : > >>if we limit our discussion to py: >>why __{get|set|delete}__ don't receive the 'name' & 'class' from >>__{getattribute|{set|del}attr}__ >>'name' is the name that is searched > > > While it would have been technically possible, I fail to imagine any use > case for this. I think he wants to have generic descriptors that are shared between multiple attributes, but have them do different things based on the attribute name. That's not the way property descriptors are designed to be used -- it's assumed that each attribute will have its own descriptor, tailored for that particular attribute. If you want to handle attributes more generically, you need to intervene at the level of __getattribute__, __getattr__ and __setattr__. -- Greg |