Skip to main content

Bringing the elegance of C# EventHandler to Python

Project description


The C# language provides a handy way to declare, subscribe to and fire events. Technically, an event is a “slot” where callback functions (event handlers) can be attached to - a process referred to as subscribing to an event. Here is a handy package that encapsulates the core to event subscription and event firing and feels like a “natural” part of the language.

>>> def something_changed(reason):
...     print "something changed because %s" % reason

>>> from events import Events
>>> events = Events()
>>> events.on_change += something_changed

Multiple callback functions can subscribe to the same event. When the event is fired, all attached event handlers are invoked in sequence. To fire the event, perform a call on the slot:

>>> events.on_change('it had to happen')
'something changed because it had to happen'

By default, Events does not check if an event can be subscribed to and fired. You can predefine events by subclassing Events and listing them. Attempts to subscribe to or fire an undefined event will raise an EventsException.

>>> class MyEvents(Events):
...     __events__ = ('on_this', 'on_that', )

>>> events = MyEvents()

# this will raise an EventsException as `on_change` is unknown to MyEvents:
>>> events.on_change += something_changed

You can also predefine events for a single Events instance by passing an iterator to the constructor.

>>> events = Events(('on_this', 'on_that'))

# this will raise an EventsException as `on_change` is unknown to events:
>>> events.on_change += something_changed


There may come a time when you no longer want to be notified of an event. In this case, you unsubscribe in the natural counterpart to += by using -=.

# We no longer want to be notified, take us out of the event callback list
>>> events.on_change -= something_changed

You may also want to unsubscribe for memory management reasons. The Events() instance will hold a reference something_changed. If this is a member method of an object, and the lifetime of the Events() instance is greater than that object, it will keep it around longer than would be the normal case.


Complete documentation is available at


Events is on PyPI so all you need to do is:

pip install events


Just run:

python test

Or use tox to test the package under all supported Pythons: 2.7, 3.4+


Events is BSD licensed. See the LICENSE for details.


Please see the Contribution Guidelines.


Based on the excellent recipe by Zoran Isailovski, Copyright (c) 2005.

Project details

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distributions

No source distribution files available for this release.See tutorial on generating distribution archives.

Built Distribution

Events-0.5-py3-none-any.whl (6.8 kB view hashes)

Uploaded Python 3

Supported by

AWS AWS Cloud computing and Security Sponsor Datadog Datadog Monitoring Fastly Fastly CDN Google Google Download Analytics Microsoft Microsoft PSF Sponsor Pingdom Pingdom Monitoring Sentry Sentry Error logging StatusPage StatusPage Status page