Python PyQt custom signal example

Last update on December 21 2024 07:44:45 (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:

Python Code Editor:

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