PyGTK3 is a popular Python library for creating graphical user interfaces (GUIs). It is based on the GTK+ 3 toolkit and provides an object-oriented interface to the GTK+ 3 library.

To use PyGTK3, you must first install it. The easiest way to do this is to use the pip package manager. To install PyGTK3, open a terminal window and type in the following command:

pip install pygtk3

Once the installation is complete, you can import the library into your Python code by using the following command:

import gi

gi.require_version(‘Gtk’, ‘3.0’)

from gi.repository import Gtk

You can then create your GUI by using the Gtk library functions. For example, to create a window, you can use the following code:

window = Gtk.Window()
window.set_title(„My Window”)
window.show_all()

Gtk.main()

You can find more information about the PyGTK3 library and its functions in the official documentation.