f2py3: 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/f2py3 - from package: python3-numpy

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

Error in other languages:
f2py3: bevel nie gevind nie
f2py3: comandă negăsită
f2py3: comando não encontrado
f2py3: commande introuvable
f2py3: command not found
f2py3: käsku ei ole
f2py3: không tìm thấy lệnh
f2py3: komanda nerasta
f2py3: Kommando nicht gefunden.
f2py3: kommandot finns inte
f2py3: komut yok
f2py3: nie znaleziono polecenia
f2py3: níor aimsíodh an t-ordú
f2py3: no se encontró la orden
f2py3: no s'ha trobat l'ordre
f2py3: opdracht niet gevonden
f2py3: parancs nem található
f2py3: perintah tidak ditemukan
f2py3: príkaz nenájdený
f2py3: příkaz nenalezen
f2py3: команда не найдена
f2py3: командата не е открита
f2py3: 命令找不到
f2py3: コマンドが見つかりません