[python/en] naming conventions and underscores

I got a bit confused about the usage of underscores so I looked it up. Made a few tweaks and added some comments based on what I found here: http://legacy.python.org/dev/peps/pep-0008/#descriptive-naming-styles.
Perhaps a tutorial like this is not the best place to bring up naming conventions, but then we should avoid cases where we have to use such naming conventions instead.
Added proposed change.