Every day, all around the world, programmers have to recycle legacy data, translate from one vendor's proprietary format into another's, check that configuration files are internally consistent, and search through web logs to see how many people have downloaded the latest release of their product. This kind of programming is usually called "data crunching," and while it may not be glamorous, knowing how to do it efficiently is essential to being a good programmer. This book describes the most useful data crunching techniques, explains when you should use them, and shows how they will make your life easier. Along the way, it will introduce you to some handy, but under-used, features of Java, Python, and other languages. It will also show you how to test data crunching programs, and how data crunching fits into the larger software development picture.