class DiscountStrategy:
    """
    This is a class that allows to use different discount strategy based on shopping credit or shopping cart in supermarket.
    """
    def __init__(self, customer, cart, promotion=None):
        self.customer = customer
        self.cart = cart
        self.promotion = promotion
        self.__total = self.total()

    def total(self):
        """
        Calculate the total cost of items in the cart.
        :return: float, total cost of items
        >>> customer = {'name': 'John Doe', 'fidelity': 1200}
        >>> cart = [{'product': 'product', 'quantity': 14, 'price': 23.5}]
        >>> ds = DiscountStrategy(customer, cart)
        >>> ds.total()
        329.0

        """

        self.__total = sum(item['quantity'] * item['price'] for item in self.cart)
        return self.__total

    @staticmethod
    def FidelityPromo(order):
        """
        Calculate the discount based on the fidelity points of the customer.Customers with over 1000 points can enjoy a 5% discount on the entire order.
        :param order: object, the order to apply the discount to
        :return: float, discount amount
        >>> customer = {'name': 'John Doe', 'fidelity': 1200}
        >>> cart = [{'product': 'product', 'quantity': 14, 'price': 23.5}]
        >>> order = DiscountStrategy(customer, cart, DiscountStrategy.FidelityPromo)
        >>> DiscountStrategy.FidelityPromo(order)
        16.45

        """

        return order.total() * 0.05 if order.customer['fidelity'] >= 1000 else 0

    @staticmethod
    def BulkItemPromo(order):
        """
        Calculate the discount based on bulk item quantity in the order.In the same order, if the quantity of a single item reaches 20 or more, each item will enjoy a 10% discount.
        :param order: object, the order to apply the discount to
        :return: float, discount amount
        >>> customer = {'name': 'John Doe', 'fidelity': 1200}
        >>> cart = [{'product': 'product', 'quantity': 20, 'price': 23.5}]
        >>> order = DiscountStrategy(customer, cart, DiscountStrategy.BulkItemPromo)
        >>> DiscountStrategy.BulkItemPromo(order)
        47.0

        """

        discount = 0
        for item in order.cart:
            if item['quantity'] >= 20:
                discount += item['quantity'] * item['price'] * 0.1
        return discount

    @staticmethod
    def LargeOrderPromo(order):
        """
        Calculate the discount based on the number of different products in the order.If the quantity of different products in the order reaches 10 or more, the entire order will enjoy a 7% discount.
        :param order: object, the order to apply the discount to
        :return: float, discount amount
        >>> customer = {'name': 'John Doe', 'fidelity': 1200}
        >>> cart = [{'product': 'product', 'quantity': 14, 'price': 23.5}]
        >>> order = DiscountStrategy(customer, cart, DiscountStrategy.LargeOrderPromo)
        >>> DiscountStrategy.LargeOrderPromo(order)
        0.0

        """

        return order.total() * 0.07 if len({item['product'] for item in order.cart}) >= 10 else 0

Method:
def due(self):
        if self.promotion is None:
            discount = 0
        else:
            discount = self.promotion(self)
        return self.__total - discount

Summary: Calculate the final amount to be paid after applying the discount.