title: How to Beautiful Soup (bs4) match just one, and only one, css class
body: <p>I am using following code to match all div that have CSS class "ad_item".</p>
  
  <pre><code>soup.find_all('div',class_="ad_item")
  </code></pre>
  
  <p>problem that I have is that, on that web page, there are also div that have CSS class set to "ad_ex_item" and "ad_ex_item".</p>
  
  <pre><code>&lt;div class="ad_item ad_ex_item"&gt;
  </code></pre>
  
  <p><a href="http://www.crummy.com/software/BeautifulSoup/bs4/doc/#searching-by-css-class" rel="nofollow">In documentation it is stated:</a></p>
  
  <blockquote>
    <p>When you search for a tag that matches a certain CSS class, you’re
    matching against any of its CSS classes:</p>
  </blockquote>
  
  <p>So how can I match div, that have only "ad_item", and do not have "ad_ex_item".</p>
  
  <p>Or to put this in another way, how to search for div that have only CSS class "ad_item" ?</p>