title: django(v2.0.1) -- _str_() method shows Object but not notes in self.text(python3.5)
body: <p>My models.py is like this:</p>
  
  <p><a href="https://i.stack.imgur.com/3N6Ks.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3N6Ks.png" alt="models.py"></a></p>
  
  <p>My python's version is 3.5.x and django version is 2.0.1, and when I went to admin's page, I got this page:</p>
  
  <p><a href="https://i.stack.imgur.com/YDmWw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/YDmWw.png" alt="enter image description here"></a></p>