blacken, lint

This pipes the file through black which silences *most* flake8
warning. The only warning left was about the `import *` which I
changed into the import of the single exception we're currently use.

Many changes are about single-quotes to double-quotes. I find those
annoying, but not as much as configuring black everywhere to not do
this. Black cannot be configured to do "the other way" (ie. only
single quotes), so then disabling this would mean not having
consistency on the quotes at all, so it's better to keep this on.

This should otherwise be a noop.