Problem python script write text file on startup

I have problem with python script. I run my python script on startup with rc.local, then, python script save some value to text file,

normally, after start up udoo provide default user is "ubuntu", i test my python script to save text file, that file will get permission is "ubuntu"

But when i start python script on startup with rc.local, after save text file then the permission of file is change to "root" and i cannot change any thing on that file, How can i fixed it?

Example rc.local to startup my python script: sudo python /home/ubuntu/mypython.py &

 

Now i can fix problem by use Crontab instance rc.local by add script to /etc/crontab as below

use command:
sudo nano /etc/crontab
in crontab add:
@reboot ubuntu python /home/ubuntu/mypython.py