Spack requires Python 2.7: from 0.18.0: (#27505)
Spack requires Python 2.7: from 0.18.0: (#27505)

* Spack requires Python 2.7: from 0.18.0:

* Better bounds
LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack