Python PyQt keyboard event handling example

Python PyQt Event Handling: Exercise-3 with Solution

Write a Python program to build a PyQt application that responds to keyboard events such as key presses and releases.

From doc.qt.io:

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

QMainWindow Class: The QMainWindow class provides a main application window.

QLabel Class: The QLabel widget provides a text or image display.

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

QKeyEvent Class: The QKeyEvent class describes a key event.

Sample Solution:

Python Code:

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QLabel, QWidget
from PyQt5.QtGui import QKeyEvent

class KeyboardEventApp(QMainWindow):
    def __init__(self):
        super().__init__()

        self.setWindowTitle("Keyboard Event Example")
        self.setGeometry(100, 100, 400, 200)

        self.central_widget = QWidget(self)
        self.setCentralWidget(self.central_widget)

        self.key_label = QLabel("Last Key Pressed: None", self.central_widget)
        self.key_label.setGeometry(10, 10, 200, 30)

    def keyPressEvent(self, event):
        if isinstance(event, QKeyEvent):
            key_text = event.text()
            self.key_label.setText(f"Last Key Pressed: {key_text}")

    def keyReleaseEvent(self, event):
        if isinstance(event, QKeyEvent):
            key_text = event.text()
            self.key_label.setText(f"Key Released: {key_text}")

def main():
    app = QApplication(sys.argv)
    window = KeyboardEventApp()
    window.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()

Explanation:

In the exercise above -

• Import the necessary PyQt5 modules.
• Create a custom class "KeyboardEventApp" that inherits from "QMainWindow".
• Inside the KeyboardEventApp class constructor (__init__), we set up the main window and a label to display keyboard events.
• Override the "keyPressEvent()" and "keyReleaseEvent()" methods to respond to key presses and releases, respectively. These methods are automatically called when keyboard events occur.
• Inside the "keyPressEvent()" and "keyReleaseEvent()" methods, we use event.text() to retrieve the text of the key that was pressed or released, and update the label with the corresponding information.
• Create an instance of the “KeyboardEventApp” class, show the main window, and start the PyQt5 application event loop.

Output:

Flowchart:

Python Code Editor:

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