title: django how to get sum of decimal in view?
body: <p>I'm using django to make website.
  I want to get total pay by members_pay</p>
  
  <p>one line of views.py</p>
  
  <pre><code>members_pay = members.aggregate(Sum('payment_amount')).get('payment_amount__sum',0.00)
  </code></pre>
  
  <p>I tried, </p>
  
  <pre><code>total = int(0)
  total += total+ memebers_pay
  </code></pre>
  
  <p>But, it occurs error 'unsupported operand type(s) for +=: 'decimal.Decimal' and 'NoneType'.
  payment_amount is demicalfield, so mayve total is NoneType.</p>
  
  <p>How I get total sum of members_pay ??</p>