Style checking

For this project, we are enforcing style guide using Flake8. This will check for things like unused variables, bad indentations, etc.

To check your code style, run:

$ flake8 .

If there are any issues with your code, you will see message(s) of the form <file-name.py>:<row-number>:<column-number>: <violation-code-and-message>. You can either manually edit your source code files to correct any formatting issues, or optionally run automatic formatting as described in the next section.