Unstated assumptions about the IAnnotations interface

[Jacob Holm]

Parts of zope 3 assume that the result of adapting an object to IAnnotations support "__contains__", "__iter__" and "items". This is true for the standard adapter(s) but is not part of the documented interface.

__contains__ is easy to implement in terms of the existing interface, so adding this to the interface is only a small burden on implementers.

__iter__ and items may be more difficult to support in some cases.

[Jacob Holm (jacobholm)]

For example, grepping for "in annotations" finds examples of all three (one false positive filtered out):

/zope3/src/optionstorage/__init__.py:
        if OptionStorageKey in annotations:
/zope3/src/optionstorage/__init__.py:
            if OptionStorageKey in annotations:
/zope3/src/zope/app/apidoc/codemodule/browser/introspector.py:
        for key, value in annotations.items():
/zope3/src/zope/app/zopeappgenerations/evolve5.py:
            if DCkey in annotations:
/zope3/src/zope/fssync/server/syncer.py:
            for key in annotations:

[Christian Theune (ctheune)]

You're right.

This appears to be a problem that people are mostly using
attribute annotations which inherit from UserDict.DictMixin.

I agree that the current situation should be changed.

I can see two ways:

1. Extend the IAnnotations interface to grow the necessary
  methods and support the existing use cases

2. Remove the ability from the existing attribute annotation
  and re-write the code that uses it to avoid using __iter__
  __contains__ and items.

Im personally in favor of option 1 because the code that uses it
IMHO proves that those methods would be useful in the interface.

Backwards-compatibility is at risk because existing IAnnotations
implementations need to supply the new methods. However, doing
so should not be too much of a burden for any IAnnotations implementation, but I might be wrong there.

I'll move the discussion to the mailinglist to find consensus for this issue.

[Christian Theune (ctheune)]

Changes: submitter email, edited transcript, topic (community => core), revised version_info, new comment

Updated version and topic.

[Christian Theune (ctheune)]

Changes: importance (medium => 3.3 Release), new comment

At least something is broken and considerably a bug. We should have *some* change in the next 3.3 release.

[Tres Seaver (tseaver)]

Added those methods to the interface in:

  https://github.com/zopefoundation/zope.annotation/commit/8113c0877a6e9f34aed20dc20968c3d2e2fde648

[Tres Seaver (tseaver)]

https://pypi.python.org/pypi/zope.annotation/4.4.0