[Zope-dev] Adding broken/missing support to zope.interface? (was: experimental.broken - Graceful handling of broken interfaces and components in the ZODB)

[Martin Aspeli]

On 9 April 2012 15:41, Brian Sutherland <brian at vanguardistas.net> wrote:

> On Sun, Apr 08, 2012 at 01:04:37PM -0700, Ross Patterson wrote:
> > experimental.broken is working well for me.  It greatly aided me in
> > getting through a particularly nasty upgrade allowing me to cleanup the
> > ZCA cruft left by poorly behaved add-ons.  I'd like to proceed with
> > adding the core of this to zope.interface and I need the
> > developers/maintainers to weigh in.
> >
> > The first and most fundamental matter is changing interface pickles such
> > that they can be unpickled into something that can fulfill the minimum
> > interface contract and don't break the ZCA.  To that end, I'd like to
> > add the following to zope.interface.interface:
> >
> >     ...
> >     try:
> >         from ZODB.broken import find_global
> >         from ZODB.broken import IBroken
> >         def find_interface(modulename, globalname,
> >                            Broken=IBroken, type=InterfaceClass):
> >             """
> >             Find a global interface, returning a broken interface if it
> can't be found.
> >             """
> >             return find_global(modulename, globalname,
> >                                Broken=IBroken, type=InterfaceClass)
> >     except ImportError:
> >         IBroken = Interface
> >         def find_interface(modulename, globalname,
> >                            Broken=IBroken, type=InterfaceClass):
> >             """
> >             Find a global interface, raising ImportError if it can't be
> found.
> >             """
> >             # From pickle.Unpickler.find_class
> >             __import__(module)
> >             mod = sys.modules[module]
> >             klass = getattr(mod, name)
> >             return klass
> >     ...
> >     class InterfaceClass(Element, InterfaceBase, Specification):
> >     ...
> >         def __reduce__(self):
> >             if self is IBroken:
> >                 return self.__name__
> >             return (find_interface, (modulename, globalname))
> >     ...
>
> -1
>
> For a number of reasons, but mainly because you add a test dependency on
> the ZODB from zope.interface. I think that zope.interface is such a
> fundamental package and the dependency is unacceptable.
>

It's a soft dependency only, looking at the code sample.


> There has lately been a LOT of work done reducing the dependency
> structure of zope.* packages. You need a VERY good reason to start
> reversing that.


 It doesn't add any more (required) dependencies.

This is a real issue that is breaking the sites of a lot of real users of
zope.interface in a way that is hard to debug and reverse.

Can you think of a better way to get around it? Other than "don't get into
the situation" which isn't a valid answer as long as the ZTK ecosystem
supports persistent local components.

Martin
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