Debugging, Testing, and Modules

Every program you write from here on will eventually break. This module covers reading Python’s errors, catching them deliberately, and inspecting code while it runs. It also covers how to check your own assumptions with automated tests, and how to split code across files with modules and reuse Python’s own standard library.

Why This Matters

Bugs aren’t a sign something’s wrong with you: they’re a constant part of writing software. Knowing what each error actually means, and how to pause your code to inspect it, turns debugging from guesswork into a process. Tests catch the bugs you’d otherwise miss on the next change. And modules are what let your code grow past a single file without becoming unmanageable.

What You’ll Learn

• How to recognize Python’s most common errors, catch them with try/except, and guarantee cleanup code runs with finally
• How to pause execution and inspect your code with a debugger, and log messages properly with the logging module
• How to write automated tests with assert and unittest
• How to accept command-line arguments with sys.argv and argparse
• How to write and import your own modules, organize several into a package, and what if __name__ == "__main__" does
• Useful built-in modules: random, math, and collections

Outcome

By the end of this module, you’ll be able to debug your own code methodically, test your assumptions automatically, and organize your code across multiple files instead of one long script.

Let’s get started.