GUI Libraries using Python - you need these to create your own graphical programs using Python. You can create your own IrfanView or Kuickshow or anything like that using the GUI libraries with their Python bindings. Bindings are what allow you to write programs in Python and use the libraries which are themselves written in C or C++ or other languages.
There are lots of choices for GUI using Python:• PyQt. This is the Python binding for the Qt toolkit which is the foundation upon which the KDE is built. Qt is extremely easy to use and very powerful especially due to the Qt Designer and the amazing Qt documentation. You can use it for free on Linux but you will have to pay for it if you want to use it on Windows. PyQt is free if you want to create free (GPL'ed) software on Linux/Unix and paid if you want to create proprietary software. A good resource on PyQt is 'GUI Programming with Python: Qt Edition' [http://www.opendocs.org/pyqt/]. See the official homepage [http://www.riverbankcomputing.co.uk/pyqt/index.php] for more details.
• PyGTK. This is the Python binding for the GTK+ toolkit which is the foundation upon which GNOME is built. GTK+ has many quirks in usage but once you become comfortable, you can create GUI apps fast. The Glade graphical interface designer is indispensable. The documentation is yet to improve. GTK+ works well on Linux but its port to Windows is incomplete. You can create both free as well as proprietary software using GTK+. See the official homepage [http://www.pygtk.org/] for more details.
• wxPython. This is the Python bindings for the wxWidgets toolkit. wxPython has a learning curve associated with it. However, it is very portable and runs on Linux, Windows, Mac and even embedded platforms. There are many IDEs available for wxPython which include GUI designers as well such as SPE (Stani's Python Editor) [http://spe.pycs.net/] and the wxGlade [http://wxglade.sourceforge.net/] GUI builder. You can create free as well as proprietary software using wxPython. See the official homepage [http://www.wxpython.org/] for more details.
• TkInter. This is one of the oldest GUI toolkits in existence. If you have used IDLE, you have seen a TkInter program at work. The documentation for TkInter at PythonWare.org [http://www.pythonware.com/library/tkinter/introduction/index.htm] is comprehensive. TkInter is portable and works on both Linux/Unix as well as Windows. Importantly, TkInter is part of the standard Python distribution.