On Jan 7, 2008, at 2:35 PM, Dieter Maurer wrote:

Dieter Maurer wrote at 2008-1-7 17:55 +0100:
Yesterday, I released "dm.zdoc" and today I find problems.

The analysis revealed:

The class "webdav.EtagSupport.EtagSupport" has initially no
attributes "__provides__" and "__providedBy__".

For still unknown reasons, it suddenly gets these attributes.
"__provides__" is a "zope.interface.declarations.ClassProvides".
Therefore, I expect that Zope 3 or "five" is responsible
for these additions.

"EtagSupport" is in the mro of "ManagableIndex".
But nevertheless, "ManagableIndex.__provides__" results in
an "AttributeError".

Here is a transscript reproducing the problem:

import App.FindHomes
from webdav.EtagSupport import EtagSupport
EtagSupport.__provides__
Traceback (most recent call last):
File "<stdin>", line 1, in ?
AttributeError: class EtagSupport has no attribute '__provides__'
from Products.ManagableIndex.ManagableIndex import ManagableIndex
/usr/local/lib/python24.zip/whrandom.py:38: DeprecationWarning: the whrandom module is deprecated; please use the random module
DeprecationWarning)
EtagSupport.__provides__
<zope.interface.declarations.ClassProvides object at 0x40b5566c>
ManagableIndex.__provides__
Traceback (most recent call last):
File "<stdin>", line 1, in ?
AttributeError: __provides__
from inspect import getmro
EtagSupport in getmro(ManagableIndex)
True


Any ideas?

I think I understand the behavior -- and I think it is a "zope.interface"
bug.

No, it is intended behavior.



Under some circumstances "zope.interface" adds a "__provides__" descriptor
to a class. The descriptor is implemented in
"zope/interface/_zope_interface_coptimizations.c" and called "CPB_descr_get".

While "__implements__" is inherited by derived classes,
the inherited "__provides__" refuses to work for a derived class
and raises "AttributeError: __provides__" instead,
the AttriuteError, I observe....

That is intentional.

I will try to make my failure independent of "ManagableIndex"
and then file a bug report.


I'm unclear why this caused a problem for you. You never said, afaict, what actually broke for you. What expectation did you have that is unsatisfied?

My main gripe with the way this works is that classes get mutated. If I ever redo this someday, I'd use a data structure external to the classes. Modifying the classes was a mistake.

Jim

--
Jim Fulton
Zope Corporation


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