A simple, yet powerful, implementation of QT's signal / slots pattern for Python3

Connectable enables you to quickly and effeciently attach actions preformed by one object, to actions of another:

from connectable import Connectable


class Person(Connectable):
    signals = ('says_hello', )

    def __init__(self, name):
        self.name = name

    def say_hello(self, to=None):
        if to:
            print("Hi {to}, this is {name}".format(to=to, name=self.name))
        else:
            print("Hi! This is {name}".format(name=self.name))
        self.emit('says_hello', self.name)


speaker = Person('Tim')
room = (Person('Amanda'), Person('Bob'), Person('Ted'), Person('Sue'))
heckler = Person('The *Real* Timothy')

for person in room:
    speaker.connect('says_hello', person.say_hello)
speaker.connect('says_hello', heckler.say_hello, transform='you horrible imposter')

speaker.say_hello()

Would output:

Hi! This is Tim
Hi Tim, this is Bob
Hi Tim, this is Sue
Hi Tim, this is Ted
Hi Tim, this is Amanda
Hi you horrible imposter, this is The *Real* Timothy

QT has a pretty good write up on the general merits of a signal / slots approach.

Making an object Connectable

To make an object Connectable, all you have to do is inherit from the Connectable class and define your signals at the class level:

from connectable import Connectable

class MyConnectable(Connectable):
    signals = ['something_changed']

Then to signal any of your defined signals, simply emit the signal name, optionally with a value:

def action(self):
    self.emit('something_changed', 'Forever.')
    # or simply self.emit('something_changed')

Then any Python method or function can be connected to that action, via the connect command:

my_object = MyConnectable()
my_object.connect('something_changed', print)

If you emitted a value and the provided slot method accepts one it will be passed as the first argument to that method.

Unique Features of Connectable

Connectable adds some additional benefits over a vanilla port of the signal / slots pattern

• You can pass a custom value to the slot:

    order_button.connect('clicked', status_label.set_text, 'Order Submitted Succesfully')

• You can add a conditional to the connection:

    edit_mode_button.connect('toggled', input_field.set_editable, True, condition=False)
    edit_mode_button.connect('toggled', input_field.set_editable, False, condition=True)

Installing connectable

Installing connectable is as simple as:

pip3 install connectable --upgrade

Ideally, within a virtual environment.

Why connectable?

I've always loved the simplicity and expressiveness of QT's take on the observer pattern, and wanted to bring a similar experience to Python.

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Thanks and I hope you find this connection helpful!

~Timothy Crosley