Python scripting with core spack

Since spack is written in python most of the internals of spack can be exposed in python scripts. Spack provides a wrapper to make this easier to deal with spack-python.

A nice trick for iterating through commands and debugging script workflows is to call spack commands in ipython. This can be done with

spack-python -c "from IPython import embed; embed()"

This will launch an ipython shell through spack-python