worker.py: 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/lib/python3/dist-packages/celery/bin/worker.py - from package: python3-celery
/usr/lib/python2.7/dist-packages/celery/bin/worker.py - from package: python-celery

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

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