Choose repositories

def choose(self):
        """Choose repositories
        """
        keys = """
Choose repositories at the right side for enable or to the
left side for disable.

Keys: SPACE   select or deselect the highlighted repositories,
             move it between the left and right lists
          ^       move the focus to the left list
          $       move the focus to the right list
        TAB     move focus
      ENTER   press the focused button

      Disabled  <-------- REPOSITORIES ------->  Enabled"""
        self.read_enabled()
        self.read_disabled()
        text, title, backtitle, status = keys, " Repositories ", "", False
        self.selected = DialogUtil(self.disabled, text, title, backtitle,
                                   status).buildlist(self.enabled)
        if self.selected is not None:
            self.update_repos()
        else:
            self.selected = self.enabled
        self.clear_screen()
        self.reference()