title: python: comparing 2 lists of instances
body: <p>I have 2 lists of instances:</p>
  
  <pre><code>list1
  list2
  </code></pre>
  
  <p>each instance contains variables such as id, name, etc...</p>
  
  <p>I am iterating through list2, and I want to find entries that don't exist in list1.</p>
  
  <p>eg..</p>
  
  <pre><code>for entry in list2:
    if entry.id in list1:
      &lt;do something&gt; 
  </code></pre>
  
  <p>I'm hoping to find a way to do this without a douple for loop.  Is there an easy way?</p>