title: SQLAlchemy arithmetic formula in where clause of update
body: <p>I'd like to do an update with a simple arithmetic expression in the where clause:</p>
  <pre><code>def update_items(self, item_type, x, y):
      table = Items.__table__
      stmt = table.update().where(table.c.item_type == item_type,
                           x - table.c.delivered &gt; y).values(available=False)
  
      with self.session_scope() as s:
          s.execute(stmt)
  </code></pre>
  <p>The problem seems to be with <code>x - table.c.delivered &gt; y</code>. I am getting an error:</p>
  <blockquote>
  <p>TypeError: where() takes 2 positional arguments but 3 were given</p>
  </blockquote>