A simple Python game based on exercise 43 in Zed Shaw's free online book Learn Python the Hard Way.
Zed uses this exercise to introduce object-oriented programming concepts to beginners.
I uploaded some previous versions of this exercise as a gist. Then later I decided to make a repo. I know that's rather backward.
Another gist: Play the alien fight scene by itself. This might be helpful for beginners.
You will see tons of comments in the code, so that's probably all you need to know.
This game should run to completion without any errors no matter what you do while playing. If you press Enter/Return without typing anything, you will die, so that's an easy way to quit.