============================
 Class-based event handlers
============================

A light-weight event-handler framework based on event classes is
provided by the ``zope.event.classhandler`` module.

Handlers are registered for event classes:

    >>> import zope.event.classhandler

    >>> class MyEvent(object):
    ...     def __repr__(self):
    ...         return self.__class__.__name__

    >>> def handler1(event):
    ...     print("handler1 %r" % event)

    >>> zope.event.classhandler.handler(MyEvent, handler1)

Descriptor syntax:

    >>> @zope.event.classhandler.handler(MyEvent)
    ... def handler2(event):
    ...     print("handler2 %r" % event)

    >>> class MySubEvent(MyEvent):
    ...     pass

    >>> @zope.event.classhandler.handler(MySubEvent)
    ... def handler3(event):
    ...     print("handler3 %r" % event)


Subscribers are called in class method-resolution order, so only
new-style event classes are supported, and then by order of registry.

    >>> import zope.event
    >>> zope.event.notify(MySubEvent())
    handler3 MySubEvent
    handler1 MySubEvent
    handler2 MySubEvent