PyQt5 - QApplication

The QApplication class manages the GUI application's control flow and main settings. It specializes in the QGuiApplication with some functionality needed for QWidget based applications. It handles widget specific initialization, finalization. For any GUI application using Qt, there is precisely one QApplication object, no matter whether the application has 0, 1, 2, or more windows at any given time. For non-QWidget based Qt applications, use QGuiApplication instead, as it does not depend on the QtWidgets library.

We then create a window instance and execute the QApplication object in the event loop using sys.exit(App.exec()) command, below are some useful and frequently methods and property used with the QApplication object.

Syntax: App = QApplication(sys.argv)

Parameters:

• beep: Sounds the bell, using the default volume and sound. This function is not available in Qt for Embedded Linux
• setFont: It sets the default font of the PyQt5 Application 
• aboutQt: Displays a simple message box about Qt. The message includes the version number of Qt being used by the application. 
• closeAllWindows: Closes all top-level windows. This function is particularly useful for applications with many top-level windows.
• setAutoSipEnabled: It automatically displays the SIP when entering widgets that accept keyboard input
• setCursorFlashTime: This method sets the text cursor's flash (blink) time in milliseconds 
• setDoubleClickInterval: This method sets the time limit in milliseconds that distinguishes a double click from two consecutive mouse clicks

Example: 

We will create a simple PyQt5 application which produces a beep sound when it gets executed and many properties are set to the QApplication object, below is the implementation

Output:
When we execute the code firstly the about Qt page will get displayed 

Then our application will get started