[Zope-dev] zope.interface: verifyObject vs properties

[Thomas Lotze]

Christian Theune <ct at gocept.com> wrote:

> Arguably, the check for an attribute would be sufficient if it checked
> whether an attribute implementation is around -- either by a simple
> attribute value or a descriptor providing that.

At this point, I guess the outcome of the discussion depends on whether
it is considered legal or abuse to implement a data descriptor in such
a way that it hides an attribute defined on a base class by raising an
AttributeError.

> There's another method: verifyClass. This definitely only checks the
> presence of an implementation. 

To be more precise: the declaration of implementation of an interface
as opposed to actual implementation of its attributes.

> Thomas: There is an issue that we regularly see with verifyClass that
> makes us instanciated the objects and then use verifyObject. I don't
> remember what it was right now. Do you?

Not really, other than to avoid the case of a happy verifyClass() call
with the application dying of a forgotten attribute implementation.
Could there be classes we subclass that claim to implement an interface
but don't fully do so until after instantiation? Just a guess...

Thomas

-- 
Thomas Lotze · tl at gocept.com
gocept gmbh & co. kg · forsterstraße 29 · 06112 halle (saale) · germany
http://gocept.com · tel +49 345 1229889 0 · fax +49 345 1229889 1
Zope and Plone consulting and development
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