Getting Started with PyQt Programming
=====================================

.. code-block:: python
   :caption: scripts/PYQT1/01_hello_world/main.py
   :linenos:

   import sys
   from PyQt5 import QtWidgets

   # Create QApplication object
   app = QtWidgets.QApplication(sys.argv)
   # Create and display the widget
   button = QtWidgets.QPushButton("Hello World!")
   button.show()
   # Start the main loop
   app.exec_()

Understanding the PyQt Main Loop
----------------------------------

- Every GUI program has a central execution loop known as the event loop. In PyQt, this is provided by the ``'QApplication'`` object. The event loop continually polls for events such as user input, and it responds according to the respective handler.

    - ``'QApplication(sys.argv)'``: To start a PyQt GUI application, a ``'QApplication'`` object must be created. ``sys.argv`` is responsible for passing command line arguments to the application.

    - ``QPushButton("Hello World!")``: Creates a button widget. Here, "Hello World!" is the text displayed on the button.

    - ``button.show()``: Displays the widget (in this case, the button) on the screen.

    - ``app.exec_()``: Starts the main event loop. This method keeps the GUI application running by continually processing events.

Creating a Simple Window
------------------------

- The example above demonstrates how to create the most basic GUI application using PyQt5.
- When you run this program, a window containing a button with the text "Hello World!" will appear.
- This window remains visible until the user clicks the close button on the window.