Traceback (most recent call last):
  File "./set_screens.py", line 37, in <module>
    screens = get_screens()
  File "./set_screens.py", line 21, in get_screens
    return [l.split()[0] for l in get("xrandr").splitlines() if " connected" in l]
  File "./set_screens.py", line 15, in get
    return subprocess.check_output(cmd).decode("utf-8")
  File "/usr/lib/python3.5/subprocess.py", line 626, in check_output
    **kwargs).stdout
  File "/usr/lib/python3.5/subprocess.py", line 708, in run
    output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command 'xrandr' returned non-zero exit status -11