The virtualenv method is not the only method to install merlin in a separate python install. The spack method will build python and all required modules for a specific set of configuration options. These options include the compiler version, system type and python version. Merlin will then be installed in this specific version allowing for multiple python versions on a single system without the need for a virtualenv. The py-merlin package builds with python3.6+.

Checkout spack

Get the latest version of spack from Github. This is independent from merlin so make sure merlin and spack are in separate directories.

git clone
# The merlin spack package is in the develop branch
git checkout develop

Setup spack

cd to spack directory

Source the or setup-env.csh. This will put spack in your path and setup module access for later use. This should be done every time the modules are used.

source ./share/spack/

Add compilers if you haven’t already:

spack compiler add

To see the compilers.

spack compiler list

Build merlin

Build merlin, this will take a long time, be prepared to wait. It will build python and all python modules merlin needs including numpy.

spack install py-merlin

The build will be done with the default compiler, in general this is the newest gcc compiler. You can choose a different compiler by using the % syntax, this will create an entirely separate build and module.

spack install py-merlin%gcc@7.1.0

A different python version can be specified as part of the package config. To build merlin with python-3.6.8 you would type:

spack install py-merlin^python@3.6.8

A tree of all of the packages and their dependencies needed to build the merlin package can be shown by using the spec keyword.

spack spec py-merlin

Activate merlin

To use merlin you can activate the module.

spack activate py-merlin


spack activate py-merlin%gcc@7.1.0


spack activate py-merlin^python@3.6.8

Load python

The associated python module can then be loaded into your environment, this will only work if you have sourced the or setup-env.csh.

module avail python

------ <path to>/spack/share/spack/modules/linux-rhel7-x86_64 -------
   python-3.6.8-gcc-8.1.0-4ilk3kn (L)

This will give you a list, the spack version will have a long hash associated with the name.

module load python-3.6.8-<compiler>-<hash>
module load python-3.6.8-gcc-8.1.0-4ilk3kn

At this point the module specific python, merlin, maestro and celery will all be in your path.