I've upgraded Lightning Compiler significantly. It is now possible to have more than one editing tab. It is now also possible to run doctest suites, with an external file. As usual, it can be found on sourceforge.
Lightning Compiler (LC) is a wxPython based app. LC's purpose is to provide a friendlier environment to tests Python code snippets than the Python interpreter. It does include an interpreter (pyShell) but it is most likely to be used for its editor. You can execute the code that appears in the editing window and the output is redirected to an output window. raw_input() and input() are handled via dialogs. The basic layout (output window to the side or below the editor window) is customisable.
LC comes in a zip file with a sample app, showing how it can be embedded in other applications, as well as a sample script with doctests and a text file containing additional doctest based tests.
Since LC uses wxPython, it can not be run with a basic Python installation. If there is some interest, I might try and adapt it so that it could use Tkinter instead (as an option. However, I have no experience with Tkinter. Any help would, of course, be appreciated :-)