pvtkpython: 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 Debian possible default full paths are:

/usr/bin/pvtkpython - from package: python-vtk6
/usr/bin/pvtkpython - from package: python-vtk

You may install the required package with command apt-get install {package}

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