Another critical e-commerce component is the payment processor, sometimes called a payment gateway or a checkout system. There are hundreds of companies offering payment solutions today. Almost all process credit cards, but some allow for "e-checks" and other more obscure payment types. These payment processors generally compete on the fees they charge per transaction. The standard rates usually involve a small fee per transaction in addition to a percentage of the transaction (usually between 1.5 percent and percent).

PayPal has historically been one of the major web-based payment processing companies and continues to process a large majority of Internet payments. There are many alternatives, however, and two of the most formidable are powered by Google and Amazon. In my opinion the latter two processors are more developer-friendly and highly recommended. Google's processor is called "Checkout" and Amazon has built a payment processor called "Flexible Payment Services" as part of their suite of web-services tools. We will build Django apps for these payment processors in Chapter 4.

The traditional means of bundling products for sale and submitting them to a payment processor involves a shopping cart. Usually, this involves the customer who selects products from the catalog web pages by adding them to their shopping cart, and then checks out with their payment method via a payment processing service. We will begin implementing a Django-based shopping cart in Chapter 3, Handling Customers and Their Orders.

Django is able to interface with these payment processing systems easily, thanks in part to the availability of tools and modules in the Python community that simplify common tasks. Python code examples and in some cases entire wrapper modules are available for many payment processing solutions. In addition, Django's template system can be used to simplify rendering of XML and other data files required to submit payment requests.

Shopping carts are also relatively simple to implement using Django. The built-in session's framework provides an easy way to store cart and checkout information between pages in a user's session. We will build our sample project on this approach later in this book.