All, To be clear, I wasn't stating that the LazyPluggable class and solution in Nova isn't good. Just that. *right now*, a few weeks before Bexar release, the best place to put this code is only in Nova. Let it bake nicely during Cactus, and we can consider really utilising the openstack-common project at that point. :)
Hope that make sense, jay On Thu, Jan 13, 2011 at 8:43 PM, Vishvananda Ishaya <vishvana...@gmail.com> wrote: > The LazyPluggable in nova common was based on yours I think. The class idea > is fine with me as long as those features are added. You just have to make > sure that you don't eat the exception in the try, catch, because that is > what import class was doing, but it was catching underlying import errors > (i.e. a missing dependency) and hiding the underlying error. > Vish > On Jan 13, 2011, at 5:30 PM, Andy Smith wrote: > > While I agree largely with the statements so far, I think the main issue > with nova-common is that the swift project and the nova project have pretty > much no communication going on between them. I think that is okay for now, > the projects are two rather distinct codebases dropped wholesale next to > each other without any prior evidence that the developers have anything in > common besides python. As things progress and there are more reasons for > people to be using both projects at once I expect that will have to start > changing. > As for lazy import, my contribution to the discussion is the LazyPluggable > class in utils.py, it is currently different from the others because it > actually lazy (rather than just runtime) and because it limits the list of > importable modules but could easily have that removed. Between importing > objects vs modules that is a pretty easy thing to ignore with a try-catch > (try first to import it as a module if that fails split the tail off and try > as an object). LazyPluggable currently does that by allowing a tuple to be > set as the module, but it is easy enough to make it just try both. > Re: class vs instance, I think class is still the way to go i the majority > of cases but it doesn't matter in practice, if you know you are expecting a > class you'll just attempt to instantiate that when you get it, but if the > string is to a function rather than a class you can still use that function > as a factory without any change to your code. > Examples of the various use cases in the ideal system: > # Code expecting a class > virt_driver = LazyPluggable(FLAGS['virt_driver']) > class ComputeManager(object): > def __init__(self): > self.virt = virt_driver() > # Above works if virt_driver points to: > # nova.virt.foo.VirtDriver > class VirtDriver(object): > pass > # or if it points to > # nova.virt.bar.VirtDriverFactory > def VirtDriverFactory(): > return VirtDriver() > > # Code expecting an instance > db_backend = LazyPluggable(FLAGS['db_backend']) > class ComputeManager(object): > def __init__(self): > self.db = db_backend > self.db.some_func() > # Above works if db_backend points to: > # nova.db.foo > def some_func(): > pass > # or if it points to > # nova.db.bar.public_api > class PublicApi(object): > def some_func(self): > pass > public_api = PublicApi() > All that functionality can be integrated into LazyPluggable trivially. > Why LazyPluggable over import_*? It is declarative, you can place it at the > top of your file and people can see all the pluggable services this file > interacts with and which flags control them. > --andy > On Thu, Jan 13, 2011 at 3:43 PM, Devin Carlen <devin.car...@gmail.com> > wrote: >> >> I see no problem with putting lazy loading in common. Just because it's >> there doesn't mean swift has to use it. Common simply implies that they are >> modules used by several, but not necessarily all, projects. >> >> >> On Jan 13, 2011, at 3:24 PM, Vishvananda Ishaya wrote: >> >> > The lazy loading in common seems fine minus one small issue. If I read >> > it correctly It looks like it is limited to a class or module. There >> > doesn't seem to be a way to proxy into an object itself. I'd like to be >> > able to specify a class (or a method) and have it lazy loaded into an >> > object >> > backend. This is what import_object did automatically that makes it so >> > versatile. Admittedly it had an annoying bug that ate underlying >> > exceptions, but imo, that is a bug that can be addressed. >> > >> > Vish >> > >> > On Jan 13, 2011, at 3:07 PM, Ewan Mellor wrote: >> > >> >> I can understand that the Swift guys don't want to destabilize their >> >> codebase, but Glance and Nova should have some common items, no? Lazy >> >> loading, logging, and I18N support all spring to mind as likely to be >> >> common >> >> across Glance and Nova. >> >> >> >> Ewan. >> >> >> >>> -----Original Message----- >> >>> From: Jay Pipes [mailto:jaypi...@gmail.com] >> >>> Sent: 13 January 2011 11:50 >> >>> To: Ewan Mellor >> >>> Cc: Todd Willey; openstack@lists.launchpad.net >> >>> Subject: Re: [Openstack] Lazy import of modules >> >>> >> >>> On Wed, Jan 12, 2011 at 6:43 PM, Ewan Mellor >> >>> <ewan.mel...@eu.citrix.com> wrote: >> >>>> At the risk of starting to shave yaks: do we want to have an >> >>> openstack-common then? It seems to be DOA at the moment. >> >>> >> >>> There's little to no agreement on common principles and code between >> >>> the projects, unfortunately. It would be best, IMHO, to just put this >> >>> in the Nova project alone. Swift coders don't have much interest in >> >>> using much of the code in Nova, and for Glance, we've used a bit of >> >>> code from Nova but will not likely be using much more, and may even >> >>> revert some of the Nova-centric stuff (like flags.py) to more >> >>> standards-based approaches used by Swift. >> >>> >> >>> -jay >> >> _______________________________________________ >> >> Mailing list: https://launchpad.net/~openstack >> >> Post to : openstack@lists.launchpad.net >> >> Unsubscribe : https://launchpad.net/~openstack >> >> More help : https://help.launchpad.net/ListHelp >> > >> > >> > _______________________________________________ >> > Mailing list: https://launchpad.net/~openstack >> > Post to : openstack@lists.launchpad.net >> > Unsubscribe : https://launchpad.net/~openstack >> > More help : https://help.launchpad.net/ListHelp >> >> >> _______________________________________________ >> Mailing list: https://launchpad.net/~openstack >> Post to : openstack@lists.launchpad.net >> Unsubscribe : https://launchpad.net/~openstack >> More help : https://help.launchpad.net/ListHelp > > > > _______________________________________________ > Mailing list: https://launchpad.net/~openstack > Post to : openstack@lists.launchpad.net > Unsubscribe : https://launchpad.net/~openstack > More help : https://help.launchpad.net/ListHelp > > _______________________________________________ Mailing list: https://launchpad.net/~openstack Post to : openstack@lists.launchpad.net Unsubscribe : https://launchpad.net/~openstack More help : https://help.launchpad.net/ListHelp
