register-python-argcomplete: 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/bin/register-python-argcomplete - from package: python-argcomplete

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

On Debian possible default full paths are:

/usr/bin/register-python-argcomplete - from package: python-argcomplete

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

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