Remove Python 2 support

Prerequisites

• pyupgrade installed (the code examples below expect it to be on the search PATH.)

Steps

The following steps are necessary to remove Python 2 support from a package:

• setup.py
  • Update version number to next major version.
  • Remove Python 2 from the list of classifiers.
  • Remove six from the list of dependencies
  • Update python_requires to python_requires='>=3.4, <4',
  • Remove other things pointing to Python 2 or PyPy[2].
• tox.ini
  • Remove py27 and pypy from `envlist
  • Remove Python 2 specific environments
• CHANGES.rst
  • Update the version number of the unreleased version
  • Add an entry: Drop support for Python 2.
• pyupgrade
  • Run find src -name "*.py" -exec pyupgrade --py3-only {} \;
    • It updates the code to Python 3 e. g. by removing (some of) six usage
  • Run grep -rn six src
    • Remove or change all the usages of six