好的，为了做到这一点，我做了以下操作：

from product.models import Discount

class AutoDiscount(Discount):
    pass

这允许我在管理区域定义不同的折扣，然后执行以下操作：

def check_automatic_discounts(sender, form=None, **kwargs):
    """
    """
    if sender in (CreditPayShipForm, SimplePayShipForm,
                  PaymentContactInfoForm):
        # I probably need to sort these in some specific order
        for discount in AutoDiscount.objects.all():
            if discount.isValid(cart=form.cart,)[0]:
                form.order.discount_code = discount.code
                form.order.save()
                return

signals.form_postsave.connect(check_automatic_discounts)

如果需要更详细地控制应用哪些折扣，我可以向AutoDiscount模型添加字段并覆盖isValid方法