MPI environment on MacOS Sierra

1. Install Xcode

Launch commands in terminal:

$ xcode-select --install

$ ln -s  ~/.bash_frofile  ~/.bashrc

2. Download the source code form  https://www.open-mpi.org/software/ompi/v2.1/    Usually you may choose openmpi-2.1.0.tar.gz

Launch commands in terminal:

$ tar zxvf openmpi-2.1.0.tar.gz

$ ./configure --prefix=/usr/local

$ make all

$ sudo make install

Then finally use     $ pip install MPI4py