[python]remove null byte "TypeError: must be string without null bytes, not str"

problems

Traceback (most recent call last):
  File "change_wallpaper.py", line 39, in <module>
    os.popen(cmd_first+' ; '+cmd)
TypeError: must be string without null bytes, not str

sol

use rstrip remove the trailling NULLs

str.rstrip('\n')