PyQt- Hello World

In this chapter, we will create a simplest PyQt GUI application which will display "Hello World" text in the widget window. To create this simple GUI application using PyQt we have to follow steps explained in this chapter.

Getting Started

Before we begin, ensure that you have PyQt installed in your Python environment. Once you have PyQt installed, you're all set to create your first PyQt application.

Steps to Create your first PyQt App

Step 1: Importing Necessary Modules

The first step is to import the required modules from PyQt. In our Hello, World! example, we need QApplication, QLabel, and QWidget. Also, we need to import the sys module to handle application termination and exit status. Let's import them −

import sys
from PyQt6.QtWidgets import QApplication, QLabel, QWidget

Step 2: Creating an Instance of QApplication

In this step we create an instance of QApplication. This is the foundation of any PyQt application −

app = QApplication([])

The QApplication class handles command-line arguments internally. In this example, we pass an empty list since our application won't be handling any command-line arguments.

Step 3: Creating the Application's GUI

In this step, we create a QWidget instance named window, which serves as the main window of our application.The setWindowTitle() method sets the title of the window.The setGeometry() method sets the size and position of the window on the screen.Then, we create a QLabel named helloMsg to display the "Hello, World!" message. The message is formatted using HTML to make it an h1 header. The move() method sets the position of the helloMsg label within the window.

window = QWidget()
window.setWindowTitle("PyQt App")
window.setGeometry(100, 100, 280, 80)
helloMsg = QLabel("
Hello, World!
", parent=window)
helloMsg.move(60, 15)

Step 4: Displaying the GUI

After creating the GUI, we need to display it using the show() method. This schedules a paint event, requesting the GUI widgets to be painted, and adds the event to the application's event queue.

window.show()

Step 5: Running the Event Loop

Finally we can run the application's event loop using the exec() method of the QApplication instance. The exec() method starts the event loop, and sys.exit() ensures a clean exit of the application when it terminates.

sys.exit(app.exec())

Step 6: Running the PyQt Application

To run your Hello, World! application, save the above code in a file named hello.py and execute it with Python −

$ python hello.py

Output

With the above steps you have written your first PyQt Application code and executed it to show the PyQt window which displays text "Hello World" message.