packages:
  all:
    compiler: [gcc]
    providers:
      mpi: [openmpi]
      blas: [openblas]
      lapack: [openblas]
  openmpi:
    version: [2.0.1]
    modules:
       [email protected]%[email protected]:  openmpi/2.0.1-gcc
    buildable: False

$ spack install dealii
Traceback (most recent call last):
  File "/spack/bin/spack", line 198, in <module>
    main()
  File "/spack/bin/spack", line 175, in main
    return_val = command(parser, args)
  File "/spack/lib/spack/spack/cmd/install.py", line 317, in install
    specs = spack.cmd.parse_specs(args.package, concretize=True)
  File "/spack/lib/spack/spack/cmd/__init__.py", line 108, in parse_specs
    spec.concretize()  # implies normalize
  File "/spack/lib/spack/spack/spec.py", line 1542, in concretize
    self._expand_virtual_packages(),
  File "/spack/lib/spack/spack/spec.py", line 1459, in _expand_virtual_packages
    spec)
  File "/spack/lib/spack/spack/concretize.py", line 122, in choose_virtual_or_external
    candidates = self._valid_virtuals_and_externals(spec)
  File "/spack/lib/spack/spack/concretize.py", line 83, in _valid_virtuals_and_externals
    externals = spec_externals(cspec)
  File "/spack/lib/spack/spack/config.py", line 489, in spec_externals
    path = get_path_from_module(module)
  File "/spack/lib/spack/spack/build_environment.py", line 149, in get_path_from_module
    modulecmd.add_default_arg('python')
AttributeError: 'NoneType' object has no attribute 'add_default_arg'