Can we dropy Python 2 support for lsst_sims?

By 2020, most of the third-party packages we know and depend on (Jupyter, astropy, etc.) will have officially dropped support for Python 2 and will release in a Python 3-only mode.

We (LSST) are also discussing dropping support for Python 2 in the near future (best estimate is that this transition is a year down the line). I would like to get a sense of how a quicker transition would impact the simulations user community, so that I have a quantitative answer to “how would dropping Python 2 affect simulations?”

If you have reservations about dropping Python 2 support by the end of spring 2018, please email me your concerns at

scottvalscott at

I will tabulate the results and pass the concerns along to the broader LSST software team.

Thank you.


I’m pro dropping Python 2 ASAP. :+1:


To clarify the approved situation, DM will stop supporting Python2 after the release of v15 in Spring 2018. Sims code will have to pin itself at v15 to retain python2 support for longer than that.