title: How do I only get values from Django queryset?
body: <p>So I have a filtered QuerySet with a specific field, that looks like this: <br>
  <code>[{'category':'book'}, {'category':'food'}, {'category':'movie'}, {'category':'book'}, {'category':'style'}, ...]</code>.
  <br>
  I now want to make a list that only contains the values(book, food, movie, style), with no duplicates. How do I make it possible? Thanks. :)</p>