[Zope-dev] Circular dependency hell.

[Christian Theune]

On 04/20/2010 08:44 PM, Jim Fulton wrote:
> On Tue, Apr 20, 2010 at 12:09 PM, Christian Theune<ct at gocept.com>  wrote:
>> Minor note: zope.testing *promotes* layers the wrong way and
>> zope.app.testing definitely implements them the wrong way.
>
> That's prety vague. Could you say specifically in what ways
> zope.testing promotes layers the wrong way and

zope.testing uses the attribute '__bases__' to store the information 
what the base layers are. __*__ are supposedly Python internal 
attributes. Specifically __bases__ is known to be used to store 
information which base classes a class has.

Looking at this I (and others too) get directed towards: aha, so layers 
are classes and use inheritance to signal what base layers are. Which is 
exactly not what is happening.

  > zope.app.testing uses them the wrong way?

Actually it doesn't. I confused this with Zope 2's Testing:

There's Testing/ZopeTestCase/layer.py which defines a class with 
classmethods and in a similar fashion there is Products.PloneTestCase 
that defines classes, derives them and thus kind of piggybacks on the 
class inheritance mechanism to establish __bases__ paired with static 
methods but without actually inheriting methods.

We struggled through some hairy details that I fail to remember when we 
worked on gocept.selenium last year which tries to establish a generic 
layer that can be combined with others. Looking at the layer code in 
gocept.selenium right now it feels relatively clean, although the exact 
choice of attribute names IMHO is confusing for anyone trying to 
understand whats going on and why.

Christian

-- 
Christian Theune · ct 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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