Python PyQt custom signal example

Last update on April 25 2025 12:51:57 (UTC/GMT +8 hours)

Write a Python program that creates a button and when clicked sends a message with a specific value. Use the PyQt module.

From doc.qt.io:

QApplication Class: The QApplication class manages the GUI application's control flow and main settings.

QWidget Class: The QWidget class is the base class of all user interface objects.

QPushButton Class: The QPushButton widget provides a command button.

Sample Solution:

Python Code:

import sys
from PyQt5.QtWidgets import QApplication, QWidget, QPushButton
from PyQt5.QtCore import pyqtSignal, QObject

class MySignalEmitter(QObject):
    # Define a custom signal with a value
    custom_signal = pyqtSignal(str)

class MyCustomWidget(QWidget):
    def __init__(self):
        super().__init__()

        # Create an instance of the signal emitter
        self.signal_emitter = MySignalEmitter()

        # Create a button
        button = QPushButton("Click Me", self)
        button.clicked.connect(self.on_button_click)

    def on_button_click(self):
        # Emit the custom signal with a value
        self.signal_emitter.custom_signal.emit("Exercises from w3resource!")

def custom_slot(value):
    print("Python PyQt:", value)

def main():
    app = QApplication(sys.argv)
    window = MyCustomWidget()
    window.setWindowTitle("Custom Signal Example")
    window.setGeometry(100, 100, 400, 200)  # (x, y, width, height)

    # Connect the custom signal to the custom slot
    window.signal_emitter.custom_signal.connect(custom_slot)

    window.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()

Explanation:

In the exercise above -

Import the necessary modules from PyQt5.
Create a custom signal emitter class "MySignalEmitter", which defines a custom signal named 'custom_signal'. This signal can send a string value when emitted.
Create a custom widget class "MyCustomWidget", which contains a button. When the button is clicked, it emits the custom_signal with the message "Exercises from w3resource!"
Define a custom slot function "custom_slot()" that receives and prints the value sent by the signal.
In the main() function, we create the PyQt application, instantiate the "MyCustomWidget" class, set the window properties, and connect the custom signal to the custom slot.

Output:

Python PyQt: Exercises from w3resource!

Flowchart:

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