Python Cookbook

Chapter 14. Debugging and Testing

Introduction

Credit: Mark Hammond, co-author of Python Programming on Win32 (O’Reilly)

The first computer I had in my home was a 64-KB Z80 CP/M machine. Having the machine available at home meant I had much more time to deeply explore this exciting toy. Turbo Pascal had just been released, and it seemed the obvious progression from the various BASIC dialects and assemblers I had been using. Even then, I was somehow drawn towards developing reusable libraries for my programs, and as my skills and employment progressed, I remained drawn to building tools that assist developers as much as building end-user applications.

Building tools for developers means that debugging and testing are often in the foreground. Although images of an interactive debugger may pop into your head, the concepts of debugging and testing are much broader than you may initially think. Debugging and testing are sometimes an inseparable cycle. Your testing will often lead you to discover bugs. You debug until you believe you understand the cause of the error and make the necessary changes. Rinse and repeat as required.

Often, debugging and testing are more insidious. I am a big fan of Python’s assert statement, and every time I use it, I am debugging and testing my program. Large projects will often develop strategies to build debugging and testing capabilities directly into the application itself, such as centralized logging and error handling. In larger projects, it could be ...