Hi all, Due to a recent change in pip and the python package index system doing $ pip install mpi4py will install mpi4py 0.6.0, a version from 2008. This is due to a recent decision to only allow pip to download packages from pypi for security reasons. I've raised this issue with the mpi4py developers so hopefully this will be fixed soon. For now, mpi4py can be installed via: pip install mpi4py --allow-external mpi4py --allow-insecure mpi4py Or by downloading the source package tarball from the mpi4py package release page on bitbucket and building manually: https://bitbucket.org/mpi4py/mpi4py/downloads Hope that avoids some confused debugging in the future, Nathan