[DM] Provide safe 'hasattr_unacquired' and 'safe_hasattr' for trusted and untrusted code.

[Andreas Jung]

2. Introduction

Formerly, Zope did not have a safe way to determine in untrusted code whether an object has a given unacquired attribute. We (at Haufe) therefore implemented an hasattr_unacquired for this function. The implementation had been donated to the Zope community (via a feature+solution collector entry) but was never added to the core.

Meanwhile, Zope allows untrusted code to safely check for unacquired attributes. It looks like hasattr(obj.aq_inner.aq_explicit, attr) -- as one can easily see: only something for insiders.

3. Feature

Define safe hasattr_unacquired and safe_hasattr and make them available for trusted and untrusted code.

4. Example Use Cases

This feature is no longer vital for us. We could rewrite all occurrences of hasattr_unacquired by the horrible expression from the introduction (which is a bit unsafe, due to hasattr peculiarities).

safe_hasattr can be emulated by means of getattr with default and a comparison against the default.

But hasattr_unacquired and safe_hasattr are a lot better to understand ;-)

[Colin Watson (cjwatson)]

The zope2 project on Launchpad has been archived at the request of the Zope developers (see https://answers.launchpad.net/launchpad/+question/683589 and https://answers.launchpad.net/launchpad/+question/685285). If this bug is still relevant, please refile it at https://github.com/zopefoundation/zope2.