Error happens while applying "chmod" to tmp file

Question

• OS: Centos7
• Language: Python
• Related Code: os.system('chmod g+w %s' % path)

• Description:

  1. I want to run this command after creating a file
  2. But when I edit and save the existing file, the OS will create the .tmp file like ~gvfSFkS.tmp and then move，this is rename，the tmp file to override the file that was edited.
  3. Here is the INFO the shell giving
     `chmod: cannot access ‘/home/share/private/student/aa/~gvfSFkS.tmp’: No such file or directory

• What I want to know

  1. The season why it happens?
  2. How I can apply chmod commad to such kind files.
• Others
  I want this python script as root.