In the following chapters, we'll explore larger-scale design considerations. Chapter 15, Design Principles and Patterns will address some general principles that can help structure the class definitions of an object-oriented program. Chapter 16, The Logging and Warning Modules will look at using the logging and warnings modules to create audit information as well as to debug. We'll look at designing for testability and how we use unittest and doctest in Chapter 17, Designing for Testability. Chapter 18, Coping with the Command Line will look at using the argparse module to parse options and arguments. We'll take this a step further and use the Command design pattern to create program components that can be combined and expanded without resorting to writing shell scripts. In Chapter 19, Module and Package Design, we'll look at module and package design. In Chapter 20, Quality and Documentation, we'll look at how we can document our design to ensure that our software is correct and is properly implemented.