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.
Ewan. > -----Original Message----- > From: Todd Willey [mailto:t...@rubidine.com] > Sent: 12 January 2011 15:03 > To: Ewan Mellor > Cc: openstack@lists.launchpad.net > Subject: Re: [Openstack] Lazy import of modules > > I ported an import behavior to openstack-common's pluggable.py, and > there is some blueprint information at > http://wiki.openstack.org/blueprint-flagged-module-loading. > > It doesn't raise it's own error, it just uses __import__, so it should > fix the problem you were seeing. I'm open to backporting it or to > actually start using openstack-common. > > -todd[1] > > On Wed, Jan 12, 2011 at 5:48 PM, Ewan Mellor > <ewan.mel...@eu.citrix.com> wrote: > > I've heard people complain that we have lots of ways of doing lazy > import of > > modules (i.e. loading them on demand, so that you don't need the > dependency > > unless you're actually using the functionality) and that we should > > standardize on one. > > > > > > > > So, which one should we standardize on? > > > > > > > > To kick the conversation off, I don't like the way that > > nova.utils.{import_object,import_class} work today, having recently > chased > > down a problem that was completely hidden by them. I had an object A > that > > was lazy-loaded using import_object, and A in turn imported B, which > was > > missing. import_object caught the ImportError for B, decided that it > meant > > that A wasn't present, attempted to import it using import_class, and > that > > failed too, and then it eventually got logged as 'Class A cannot be > found'. > > This was wrong firstly because A was not missing, and secondly > because A > > wasn't a class, and thirdly because the code didn't ask to import it > as a > > class! There was no indication that B was missing. > > > > > > > > This took me a long time to unpick, so if we're going to standardize > around > > nova.utils.import_x, then we need to figure out a better way for them > to > > work. > > > > > > > > Thanks, > > > > > > > > Ewan. > > > > > > > > def import_class(import_str): > > > > """Returns a class from a string including module and class""" > > > > mod_str, _sep, class_str = import_str.rpartition('.') > > > > try: > > > > __import__(mod_str) > > > > return getattr(sys.modules[mod_str], class_str) > > > > except (ImportError, ValueError, AttributeError), exc: > > > > logging.debug(_('Inner Exception: %s'), exc) > > > > raise exception.NotFound(_('Class %s cannot be found') % > class_str) > > > > > > > > def import_object(import_str): > > > > """Returns an object including a module or module and class""" > > > > try: > > > > __import__(import_str) > > > > return sys.modules[import_str] > > > > except ImportError: > > > > cls = import_class(import_str) > > > > return cls() > > > > > > > > _______________________________________________ > > Mailing list: https://launchpad.net/~openstack > > Post to : openstack@lists.launchpad.net > > Unsubscribe : https://launchpad.net/~openstack > > More help : https://help.launchpad.net/ListHelp > > > > > > > > -- > CONFIDENTIALITY NOTICE: This email is for sole use of intended > recipient(s). Unauthorized use is prohibited. _______________________________________________ Mailing list: https://launchpad.net/~openstack Post to : openstack@lists.launchpad.net Unsubscribe : https://launchpad.net/~openstack More help : https://help.launchpad.net/ListHelp
