Object-Oriented Programming/GUI Applications/Hello World

"""This program displays "Hello world!" using object-oriented Python and
    tkinter.

Input:
    None

Output:
    Hello world!

References:
    https://www.geeksforgeeks.org/hello-world-in-tkinter/
    https://www.tutorialspoint.com/python/python_gui_programming.htm
    https://www.python-course.eu/python_tkinter.php
"""

import tkinter


class Root(tkinter.Tk):
    """Creates root window."""

    def __init__(self, *args, **kwargs):
        tkinter.Tk.__init__(self, *args, **kwargs)
        label = tkinter.Label(
            text="Hello world!",
            width=320,
            height=240)
        label.pack()


if __name__ == "__main__":
    root = Root()
    root.mainloop()