[Zope-dev] Bad idiom to access optional attributes

[Dieter Maurer]

I just analysed why "AccessControl.Role.RoleManager.get_valid_userids"
raised an unexpected "AttributeError".

It uses the wrong idiom to access optional attribute:

   aclu = getattr(aq_base(item), '__allow_groups__', _notfound)

This means, that "aclu" is only partially acquisition wrapped
and does not behave as usual.

Until Tim reported that "hasattr" behaves bad with respect
to exceptions, I have been convinved, that the following
idiom were correct:

      if hasattr(aq_base(obj), attrname):
          attr = getattr(obj, attrname)
	  ...

Meanwhile, the best way to access optional attributes seems to be

      if getattr(aq_base(obj), attrname, notFound) is not notFound:
          attr = getattr(obj, attrname)
	  ...


Please keep this in mind when you push the
"Death to 'hasattr'" project.

-- 
Dieter