title: sqlalchemy filter by comparing datetime.now() and column default date
body: <p>in my table definition, i have a column defined like this:</p>
  
  <pre><code>created_date = Column(DateTime, nullable=False, default=datetime.now)
  </code></pre>
  
  <p>i want to query a instance when its created date is equal to current date(eg, if it is created today).</p>
  
  <p>so i tried something like this:</p>
  
  <pre><code>res = session.query(Object).filter(datetime.now() == Object.created_date)
  </code></pre>
  
  <p>it never works because two dates are compared in seconds i guess, so they will never be equal to each other. then i tried this:</p>
  
  <pre><code>res = session.query(Object).filter((datetime.now() - Object.created_date).days &lt; 1)
  </code></pre>
  
  <p>while <code>(datetime.now() - datetime.now()).days</code> works in python, it doesnt work in my situation here. i got error says: Neither 'BinaryExpression' object nor 'Comparator' object has an attribute 'days'.</p>
  
  <p>So how should i do a query that filters instances created on a current day? thanks!</p>