Classhandler

CHANGES.rst

@@ -1,11 +1,11 @@
 ``zope.event`` Changelog
 ========================
 
-4.0.4 (unreleased)
+4.1.0 (unreleased)
 ------------------
 
 - Require 100% branch (as well as statement) coverage.
-
+- Added a simple class-based handler implementation.
 
 4.0.3 (2014-03-19)
 ------------------

docs/classhandler.rst

@@ -0,0 +1,42 @@
+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
+

docs/index.rst

@@ -19,6 +19,7 @@ Contents:
    usage
    theory
    api
+   classhandler
    hacking
 
 Indices and tables

src/zope/event/classhandler.py

@@ -0,0 +1,70 @@
+"""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)

src/zope/event/tests.py

@@ -13,6 +13,7 @@
 ##############################################################################
 """ Test the event system
 """
+import doctest
 import unittest
 
 class Test_notify(unittest.TestCase):
@@ -42,7 +43,18 @@ def test_not_empty(self):
         self._callFUT(event)
         self.assertEqual(dummy, [event])
 
+def setUpClassHandlers(test):
+    import zope.event
+    test.globs['old_subs'] = zope.event.subscribers
+
+def tearDownClassHandlers(test):
+    import zope.event
+    zope.event.subscribers = test.globs['old_subs']
+
 def test_suite():
     return unittest.TestSuite((
         unittest.makeSuite(Test_notify),
+        doctest.DocTestSuite(
+            'zope.event.classhandler',
+            setUp=setUpClassHandlers, tearDown=tearDownClassHandlers)
         ))