Class Event

Special descriptor for class __provides__

The descriptor caches the implementedBy info, so that
we can get declarations for objects without instance-specific
interfaces a bit quicker.

For example:

  >>> from zope.interface import Interface
  >>> class IFooFactory(Interface):
  ...     pass
  >>> class IFoo(Interface):
  ...     pass
  >>> class C(object):
  ...     implements(IFoo)
  ...     classProvides(IFooFactory)
  >>> [i.getName() for i in C.__provides__]
  ['IFooFactory']

  >>> [i.getName() for i in C().__provides__]
  ['IFoo']