If your web application's success depends on how quickly and easily users can make transactions, PayPal APIs provide effective solutions you can't afford to overlook. This concise book takes you hands-on through several options to help you determine the best choice for your situation, whether you're collecting money via websites or mobile apps for products and services, donations, or anything else. In each chapter, you'll work with a different PayPal API by integrating it into the book's sample application, using Python and the Google App Engine framework. This expanded edition introduces two new options: Express Checkout for Digital Goods and Instant Payment Notifications, complete with sample project code. By the end of this book, you'll understand how to take full advantage of PayPal and its powerful features.Learn PayPal API basics, and get an introduction to Google App Engine Explore the Express Checkout option, and understand what distinguishes it from other generic workflows Tailor Express Checkout for electronic documents, videos, and other "in app" digital purchases Apply the Adaptive Payments option for transactions that involve multiple recipients Embed the payment process into your site with no mention of PayPal, using Website Payments Pro Use the Instant Payment Notifications you receive as triggers to take follow-up action