title: How calculate the total price of a product attribute
body: <pre><code>class attributes(models.Model):
  
          attribute_name = models.CharField(max_length = 200, db_index = True)
          price_update = models.DecimalField(max_digits = 10, 
                                         decimal_places = 2)
  
  
  class Product(models.Model):
  
          attribute = models.ManyToManyField(attributes)
  </code></pre>