python-mpi: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/lib64/python2.6/site-packages/mpich/mpi4py/bin/python-mpi - from package: mpi4py-mpich
/usr/lib64/python2.6/site-packages/openmpi/mpi4py/bin/python-mpi - from package: mpi4py-openmpi

You may install the required package with command yum install {package}

Error in other languages:
python-mpi: bevel nie gevind nie
python-mpi: comandă negăsită
python-mpi: comando não encontrado
python-mpi: commande introuvable
python-mpi: command not found
python-mpi: käsku ei ole
python-mpi: không tìm thấy lệnh
python-mpi: komanda nerasta
python-mpi: Kommando nicht gefunden.
python-mpi: kommandot finns inte
python-mpi: komut yok
python-mpi: nie znaleziono polecenia
python-mpi: níor aimsíodh an t-ordú
python-mpi: no se encontró la orden
python-mpi: no s'ha trobat l'ordre
python-mpi: opdracht niet gevonden
python-mpi: parancs nem található
python-mpi: perintah tidak ditemukan
python-mpi: príkaz nenájdený
python-mpi: příkaz nenalezen
python-mpi: команда не найдена
python-mpi: командата не е открита
python-mpi: 命令找不到
python-mpi: コマンドが見つかりません