Help with run commands from a python script

[snippsat]

If pass in a string command need shell=True.
Better and safer to pass in a list.
Can try:

import subprocess

subprocess.Popen([r'C:\Program Files\Blender Foundation\Blender\blender.exe', 'untitled', '02.blend', '-b', '-a'])

If you use blender some should also add it to Windows Path.
Then can call just blender.

import subprocess

subprocess.Popen(['blender', 'untitled', '02.blend', '-b', '-a'])