python-dispatch 0.0.9

Lightweight Event Handling

Lightweight event handling for Python

Description

This is an implementation of the “Observer Pattern” with inspiration from the Kivy framework. Many of the features though are intentionally stripped down and more generalized. The goal is to have a simple drop-in library with no dependencies that stays out of the programmer’s way.

Installation

pip install python-dispatch

Usage

For more information, see the documentation here: https://nocarryr.github.io/python-dispatch

Events

from pydispatch import Dispatcher

class MyEmitter(Dispatcher):
    # Events are defined in classes and subclasses with the '_events_' attribute
    _events_ = ['on_state', 'new_data']
    def do_some_stuff(self):
        # do stuff that makes new data
        data = self.get_some_data()
        # Then emit the change with optional positional and keyword arguments
        self.emit('new_data', data=data)

# An observer - could inherit from Dispatcher or any other class
class MyListener(object):
    def on_new_data(self, *args, **kwargs):
        data = kwargs.get('data')
        print('I got data: {}'.format(data))
    def on_emitter_state(self, *args, **kwargs):
        print('emitter state changed')

emitter = MyEmitter()
listener = MyListener()

emitter.bind(on_state=listener.on_emitter_state)
emitter.bind(new_data=listener.on_new_data)

emitter.do_some_stuff()
# >>> I got data: ...

emitter.emit('on_state')
# >>> emitter state changed

Properties

from pydispatch import Dispatcher, Property

class MyEmitter(Dispatcher):
    # Property objects are defined and named at the class level.
    # They will become instance attributes that will emit events when their values change
    name = Property()
    value = Property()

class MyListener(object):
    def on_name(self, instance, value, **kwargs):
        print('emitter name is {}'.format(value))
    def on_value(self, instance, value, **kwargs):
        print('emitter value is {}'.format(value))

emitter = MyEmitter()
listener = MyListener()

emitter.bind(name=listener.on_name, value=listener.on_value)

emitter.name = 'foo'
# >>> emitter name is foo
emitter.value = 42
# >>> emitter value is 42