Interactive PyQt Signal Tutorial

Welcome to this interactive tutorial on creating, emitting, and connecting signals in PyQt. In this tutorial, you will learn how to create custom signals, emit them, and connect signal(s) to slots in your PyQt application.

Creating a Signal

To create a custom signal in PyQt, we use the pyqtSignal() function. The syntax for creating a signal is:

    signal = pyqtSignal(arg_type1, arg_type2, ...)

For example, the following code creates a signal named dataChanged that takes a single argument of type int:

    dataChanged = pyqtSignal(int)

Emitting a Signal

To emit a signal, we use the emit() function. The syntax for emitting a signal is:

    signal.emit(arg1, arg2, ...)

For example, to emit the dataChanged signal with a value of 42, we would use the following code:

    dataChanged.emit(42)

Connecting a Signal to a Slot

To connect a PyQt signal to a slot, use the connect() method. The syntax for connecting a signal to a slot is:

    signal.connect(slot_function)

For example, to connect the dataChanged signal to a slot_function, we would use the following code:

    dataChanged.connect(slot_function)

It's worth noting that the slot function should have the same number and type of arguments as the signal

Example

Let's put everything together in a simple example. In this example, we will create a custom signal named dataChanged and connect it to a slot that prints the new data value.

from PyQt6.QtCore import pyqtSignal, QObject

class MyData(QObject):

    dataChanged = pyqtSignal(int)

    

    def __init__(self, data=0):

        super().__init__()

        self._data = data

    

    @property

    def data(self):

        return self._data

    

    @data.setter

    def data(self, new_data):

        self._data = new_data

        self.dataChanged.emit(new_data)

def slot_function(data):

    print("Data changed to", data)

In this example, we created a custom class called MyData which inherits from QObject. Within this class, we create a signal called dataChanged using the pyqtSignal() function and taking an argument of type int. We also create a data property which holds the current data value, and a data.setter method which updates the data and emits the dataChanged signal with the new data value. Next, we define the slot_function that will be called when the dataChanged signal is emitted. In this case, it takes the new data value as an argument and prints "Data changed to [new_data]"

Finally, to use this class and connect the signal to the slot, you would use the following code:

my_data = MyData()

my_data.dataChanged.connect(slot_function)

my_data.data = 42

Now, every time the data attribute is set to a new value, it will emit the dataChanged signal, which will in turn call the slot_function and print "Data changed to 42"

Summary

In this tutorial, you learnt how to create, emit, and connect signals in PyQt. You learned how to create custom signals, emit them, and connect them to slots in your PyQt application. With this knowledge, you should be able to create your own signals, and use them to make your application more responsive and dynamic.

I hope you found this tutorial helpful. If you have any questions or comments, please feel free to leave them below.