title: Django: how to check if Q object is empty?
body: <p>I am chaining nodes to a <code>Q</code> object the following way:</p>
  
  <pre><code>q = Q()
  for filter in filters:
      if filter_applies(filter):
          q.add(Q(some_criteria), Q.OR)
  </code></pre>
  
  <p>What means the <code>q</code> object might or might not have been chained a node. Later on I am trying to apply the <code>q</code> object in a filter, but only if this is not <em>empty</em>:</p>
  
  <pre><code>if q.not_empty():
      some_query_set.filter(q)
  </code></pre>
  
  <p>How can I check that <code>q</code> is not the same than it was when defined?</p>