This chapter is essentially a continuation of the previous one, which introduced Express Checkout. However, whereas the previous chapter established the fundamentals of Express Checkout and implemented a routine checkout for the Tweet Relevance reference application that’s featured in Appendix A, this chapter works through the implementation details of a much more highly specialized checkout that can be used for situations involving “in-app” purchases of digital goods such as electronic documents, audio files, videos, or—you guessed it—items such as login tokens for Tweet Relevance using a derivative of Express Checkout called Express Checkout for Digital Goods. Of all of the PayPal products featured in this book, Express Checkout for Digital Goods is possibly the best fit for processing Tweet Relevance payments since Tweet Relevance is inherently a digital good. (Processing digital goods transactions with Adaptive Payments is probably the other best option.)
PayPal’s official documentation for Express Checkout for Digital Goods is available online: Express Checkout for Digital Goods Developer Guide.
The sample code for this chapter builds upon the sample project from the previous chapter involving a traditional Express Checkout. It is highly recommended that you read that chapter first and be familiar with the implementation details in PaymentHandler.py.
It hasn’t always been the case ...