This patch contains mostly-automated refactorings to remove code that
we only needed to support Python 2. Since Hypothesis is now Python 3
only (hurray!), there is no user-visible change.
Our sincere thanks to the authors of autoflake, black, isort, and
pyupgrade, who have each and collectively made this kind of update
enormously easier.
The canonical version of these notes (with links) is on readthedocs.