Dropping support for Python 2.6

[Giovanni]

Hi Everyone,

It's been a while since I brought up the topic, but it's time to drop support for Python 2.6 from PySlurm. The open source community has long dropped support for it. In fact, the Python community will stop supporting Python 2 on Jan 1, 2020. Many other projects have pledged to drop all support for Python2, including Numpy, Scipy and Jupyter Notebooks just to name a few (https://python3statement.org/).

I will stop testing PySlurm against Python 2.6. Given the EOL statement, Python 2.7 support will also need to be phased out. PySlurm has fully supported Python 3 for about two years now.

Please feel free to share any concerns.

Thanks,

Giovanni