python简单实现计算过期时间的方法

def time_passed(value):
  now = datetime.now()
  past = now - value
  if past.days:
    return u'%s天前' % past.days
  mins = past.seconds / 60
  if mins < 60:
    return u'%s分钟前' % mins
  hours = mins / 60
  return u'%s小时前' % hours