Revision 18 is missing the editdist module and its distance function. Example traceback:

$ python Amphetype.py

Traceback (most recent call last): File "Amphetype.py", line 14, in <module> from Lesson import LessonGenerator File "Lesson.py", line 8, in <module> import editdist ImportError: No module named editdist

By the way, when I supply my own version of this module, the program works correctly on Linux.

Fixed. Made a fake editdist that it imports if you don't have py-editdist. Wrote about it in the readme.txt as an optional module.