twisted.words.xish.utility.EventDispatcher : API documentation

Event dispatching service.

The EventDispatcher allows observers to be registered for certain events that are dispatched. There are two types of events: XPath events and Named events.

Every dispatch is triggered by calling dispatch with a data object and, for named events, the name of the event.

When an XPath type event is dispatched, the associated object is assumed to be an Element instance, which is matched against all registered XPath queries. For every match, the respective observer will be called with the data object.

A named event will simply call each registered observer for that particular event name, with the data object. Unlike XPath type events, the data object is not restricted to Element, but can be anything.

When registering observers, the event that is to be observed is specified using an xpath.XPathQuery instance or a string. In the latter case, the string can also contain the string representation of an XPath expression. To distinguish these from named events, each named event should start with a special prefix that is stored in self.prefix. It defaults to //event/.

Observers registered using addObserver are persistent: after the observer has been triggered by a dispatch, it remains registered for a possible next dispatch. If instead addOnetimeObserver was used to observe an event, the observer is removed from the list of observers after the first observed event.

Observers can also be prioritized, by providing an optional priority parameter to the addObserver and addOnetimeObserver methods. Higher priority observers are then called before lower priority observers.

Finally, observers can be unregistered by using removeObserver.

def addObserver(self, event, observerfn, *args, priority=0, **kwargs): (source)

Each observer will be registered with a certain priority. Higher priority observers get called before lower priority observers.

Parameters	event	Name or XPath query for the event to be monitored. (type: `str` or `xpath.XPathQuery`.)
	observerfn	Function to be called when the specified event has been triggered. This callable takes one parameter: the data object that triggered the event. When specified, the `args` and `*kwargs` parameters to addObserver are being used as additional parameters to the registered observer callable.
	priority	(Optional) priority of this observer in relation to other observer that match the same event. Defaults to `0`. (type: `int`)

def dispatch(self, obj, event=None): (source)

Dispatch an event.

When event is None, an XPath type event is triggered, and obj is assumed to be an instance of Element. Otherwise, event holds the name of the named event being triggered. In the latter case, obj can be anything.

Parameters	obj	The object to be dispatched.
	event	Optional event name. (type: `str`)

Method	__init__	Undocumented
Method	addOnetimeObserver	Register a one-time observer for an event.
Method	addObserver	Register an observer for an event.
Method	removeObserver	Remove callable as observer for an event.
Method	dispatch	Dispatch an event.
Method	_getEventAndObservers	Undocumented
Method	_addObserver	Undocumented

Parameters	event	Event for which the observer callable was registered. (type: `str` or `xpath.XPathQuery`)
	observerfn	Observer callable to be unregistered.

t.w.x.u.EventDispatcher : class documentation