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Edit File: classhandler.py

"""Class-based event handlers

A light-weight event-handler framework based on event classes.

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

"""
import zope.event

registry = {}

def handler(event_class, handler_=None, decorator=False):
    """Define an event handler for a (new-style) class.

This can be called with a class and a handler, or with just a
    class and the result used as a handler decorator.
    """
    if handler_ is None:
        return lambda func: handler(event_class, func, True)

if not registry:
        zope.event.subscribers.append(dispatch)

if event_class not in registry:
        registry[event_class] = [handler_]
    else:
        registry[event_class].append(handler_)

if decorator:
        return handler

def dispatch(event):
    for event_class in event.__class__.__mro__:
        for handler in registry.get(event_class, ()):
            handler(event)

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