Signals and Slots (registering callbacks)

If a served object exposes a Qt signal (or Qt-like signals), you can connect a slot to it in the proxy. If you are not familiar with the Qt jargon, this is equivalent to bind (connect) a callback (slot) to an event (signal).

The syntax in the client side is exactly as it is done in PyQt/PySide New Style Signals and Slots:

def print_notification(new_position):
    print('The arm has been moved to {}'.format(new_position))

proxy = Proxy('tcp://127.0.0.1:8000')

proxy.arm_moved.connect(print_notification)

Under the hood, the proxy is subscribing to an event in the server using a ZMQ SUB socket. When the arm_moved signal is emitted server-side, the server will asynchronously notify the proxy using a PUB socket. The proxy will call print_notification when it receives message. So you have client side notification of server side events.

It is important to note that if you are using PyQt/PySide signals in your code, no modification is needed to use Pizco. But not only PyQt/PySide signals work. An attribute is considered Signal if it exposes at least three methods: connect, disconnect and emit.

Just like PyQt, multiple slots can be connected to the same signal:

proxy.arm_moved.connect(print_notification)
proxy.arm_moved.connect(mail_notification)

and they will be called in the order that they were added.

To disconnect from a signal:

proxy.arm_moved.disconnect(mail_notification)

Additionally, you can connect in another proxy:

proxy2 = Proxy('tcp://127.0.0.1:8000')

proxy2.arm_moved.connect(mail_notification)

Proxy connections to signals are independent and therefore disconnecting in one proxy will not have an effect on another.