I have installed the latest available weekly of
w_2017_48 from source and I get Python v3.6.2 installed:
$ source loadLSST.bash
$ python --version
Python 3.6.2 :: Continuum Analytics, Inc.
For my installations I always use the version of
newinstall.sh in the
master branch, i.e.
However, I have not installed
lsst_sims, so this suggestion may not solve your issue.