Set up textedit to save python files (help me please)

Guys, I need a little help. Since last week I'm trying to set up text edit to start using python on Mac. But everytime I save any file with .py extension, it changes to blabla.py.rtf and have to choose maintain both extensions or only rtf/ txt. I checked textedit preferences and couldn't get it to work. I don't want to use third-party apps.