Python cookbook

It works on your machine. It breaks on theirs.

Print statements are fine for a five-line script and useless once the codebase grows past a page.

Someone hands you a CSV file you've never opened, and you have no idea what's actually inside it.

You've got a clean CSV export, and the system you're sending it to only takes JSON.

Some customer names arrive in ALL CAPS, some have extra spaces, and the emails mix upper and lower case throughout the file.

Your script processes ten thousand rows fine until one row has a missing value, and the whole run dies right there.

You call an API, parse the reply immediately, and a bug in your own parsing means calling that same API all over again.

Your script only runs because a file path is typed straight into the source code, and nobody else on the team can point it anywhere else.

One script does everything at once: fetch, clean, and save, and you can't check any single part without running the whole thing.