Small python module that implements the observer pattern via a decorator.
Deprecation notice
This module has been unmaintained since around 2014. The authors have moved on to other alternatives to event handling. There is also observed by @DanielSank, which was partially inspired by obsub, however, has not seen many updates lately. @milibopp has been writing with functional reactive programming (FRP), but not for Python.
FRP is a higher-level abstraction than the observer pattern, that essentially is a purely functional approach to unidirectional dataflow, composing your programs of event stream transformations. Experience has shown, that is easier to compose and to test than the raw observer pattern. A solid implementation in Python is RxPY, part of the ReactiveX project.
This is based on a thread on stackoverflow (the example of C#-like events by Jason Orendorff), so I don't take any credit for the idea. I merely made a fancy module with documentation and tests out of it, since I needed it in a bigger project. It is quite handy and I've been using it in a couple of projects, which require some sort of event handling.
Thus it is licensed as CC0, so basically do-whatever-you-want to the extent legally possible.
obsub is available on PyPI, so you can simply install it using
pip install obsub or you do it manually using setup.py as with
any python package.
The event decorator from the obsub module is used as follows:
from obsub import event
# Define a class with an event
class Subject(object):
@event
def on_stuff(self, arg):
print('Stuff {} happens'.format(arg))
# Now define an event handler, the observer
def handler(subject, arg):
print('Stuff {} is handled'.format(arg))
# Wire everything up...
sub = Subject()
sub.on_stuff += handler
# And try it!
sub.on_stuff('foo')You should now get both print messages from the event itself and the event handler function, like so:
Stuff foo happens Stuff foo is handled
obsub is developed on github.
If you have any questions about this software or encounter bugs, you're welcome to open a new issue on github.
In case you do not want to use github for some reason, you can alternatively send an email one of us:
Feel free to contribute patches as pull requests as you see fit. Try to be consistent with PEP 8 guidelines as far as possible and test everything. Otherwise, your commit messages should start with a capitalized verb for consistency. Unless your modification is completely trivial, also add a message body to your commit.
Thanks to Jason Orendorff on for the idea on stackoverflow. I also want to thank @coldfix and @Moredread for contributions and feedback.