Python in a Nutshell, 3rd Edition

Chapter 16. Testing, Debugging, and Optimizing

You’re not finished with a programming task when you’re done writing the code; you’re finished when the code runs correctly, with acceptable performance. Testing (covered in “Testing”) means verifying that code runs correctly, by automatically exercising the code under known conditions and checking that results are as expected. Debugging (covered in “Debugging”) means discovering causes of incorrect behavior and repairing them (repair is often easy, once you figure out the causes).

Optimizing (covered in “Optimization”) is often used as an umbrella term for activities meant to ensure acceptable performance. Optimizing breaks down into benchmarking (measuring performance for given tasks to check that it’s within acceptable bounds), profiling (instrumenting the program with extra code to identify performance bottlenecks), and optimizing proper (removing bottlenecks to make overall program performance acceptable). Clearly, you can’t remove performance bottlenecks until you’ve found out where they are (using profiling), which in turn requires knowing that there are performance problems (using benchmarking).

This chapter covers the subjects in the natural order in which they occur in development: testing first and foremost, debugging next, and optimizing last. Most programmers’ enthusiasm focuses on optimization: testing and debugging are often (wrongly, in our opinion) perceived as being chores, while optimization is seen as being fun. ...