Python Cookbook, 2nd Edition

Chapter 8. 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 at home meant I had much 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 drawn towards developing reusable libraries for my programs, and as my skills and employment experience progressed, I remained drawn to building tools that assisted 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. Testing will often lead to the discovery of bugs. You debug until you believe you understand the cause of the error and make the necessary changes. Rinse and repeat as required.

Debugging and testing often 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 often develop strategies to build debugging and testing capabilities directly into the application itself, such as centralized logging and error handling. It could be argued that this style of debugging and ...