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Signals and Slots. PySide and PyQt are Python bindings to the Qt GUI and application framework. One killer feature of Qt is the signal & slot system, which is a way for widgets and objects to communicate events to one another. An object in Qt can send a signal to other subscribed objects. Signals are used to inform other objects that an event.

I was to lazy to take a look at the

1. PyQt5 - Signal and slot function The signal and slot operation are used to handle events and signals of the objects or widgets at the python app development level. It will also enable communication between some designed objects. The following steps are needed for creating a Python signal and slot operations.
2. PyQt5 uses a unique signal and slot mechanism to handle events. Signals and slots are used for communication between objects, and when a particular event occurs, the signal is fired. The slot can be any Python call. The connection to the slot is called while the signal is transmitting.
3. Buttons (QPushButton) can be added to any window. The QPushButton class has the method setText for its label and move(x,y) for the position. In this article you can see how a button can be added to a window, and how you can connect methods to it. Related Course: Create GUI Apps with Python PyQt5. PyQt Button Example Signals.
4. QtCore.SIGNAL and QtCore.SLOT macros allow Python to interface with Qt signal and slot delivery mechanisms. This is the old way of using signals and slots. The example below uses the well known clicked signal from a QPushButton. The connect method has a non python-friendly syntax.

new-style signal and slot support which was introduced in PyQt 4.5 until yesterday. I did know that there were something called new-style signals and slots but that was the end of the story. Now I have taken the time and I think it's a cleaner solution than the old-style.
I'll just give you a short intro to whet your appetite, find all details here yourself.

Python Pyqt Signals Slot Machine

This is the old way of connecting a signal to a slot. To use the new-style support just replace line 11 with following code
The

Python Qt Signals Slots

new-style support introduces an attribute with the same name as the signal, in this case

Python Pyqt Signal Slot

clicked.
If you need to define your own signal you'll do something like this (off the top of my head):
And the old way:
IMHO the new-style support is more pythonic and you don't have to specify your signals as strings when connecting. If you use pydev (eclipse) you'll also have completion support for signals.