Creating and Sending Events¶
As discussed in Quick Start, most uses of
zope.lifecycleevent will be satisfied with the high level API
IZopeLifecycleEvent, but it is
possible to create and send events manually, both those defined here
and your own subclasses.
All of the functions described in Quick Start are very simple
wrappers that create an event object defined by this package and then
zope.event.notify() to send it. You can do the same, as
shown below, but there is usually little reason to do so.
>>> from zope.event import notify >>> from zope.lifecycleevent import ObjectCreatedEvent >>> from zope.lifecycleevent import ObjectCopiedEvent >>> from zope.lifecycleevent import ObjectModifiedEvent >>> from zope.lifecycleevent import ObjectMovedEvent >>> from zope.lifecycleevent import ObjectRemovedEvent
>>> obj = object() >>> notify(ObjectCreatedEvent(obj)) >>> notify(ObjectCopiedEvent(object(), obj)) >>> notify(ObjectMovedEvent(obj, ... None, 'oldName', ... None, 'newName')) >>> notify(ObjectModifiedEvent(obj, "description 1", "description 2")) >>> notify(ObjectRemovedEvent(obj, "oldParent", "oldName"))
It can sometimes be helpful to subclass one of the provided event classes. If you then want to send a notification of that class, you must manually construct and notify it.
One reason to create a subclass is to be able to add additional
attributes to the event object, perhaps changing the constructor
signature in the process. Another reason to create a subclass is to be
able to easily subscribe to all events that are just of that class.
used for this reason.
For example, in an application with distinct users, we might want to let subscribers know which user created the object. We might also want to be able to distinguish between objects that are created by a user and those that are automatically created as part of system operation or administration. The following subclass lets us do both.
>>> class ObjectCreatedByEvent(ObjectCreatedEvent): ... "A created event that tells you who created the object." ... def __init__(self, object, created_by): ... super(ObjectCreatedByEvent, self).__init__(object) ... self.created_by = created_by
>>> obj = object() >>> notify(ObjectCreatedByEvent(obj, "Black Night"))