Every Friday, you'll get a recap of the most important and exciting Python and coding news. The Friday Loop also keeps everyone posted on new ArjanCodes courses and any limited offers coming up.
DeepSeek Won't Matter for Software Engineers | Issue #38
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​The Friday Loop
Every Friday, you'll get a recap of the most important and exciting Python and coding news. The Friday Loop also keeps everyone posted on new ArjanCodes courses and any limited offers coming up.
In a recent video on refactoring complicated business logic, I managed to introduce several subtle errors. Many of you immediately spotted them in the comments. That’s exactly what my first video in 2026 is about. I walk through the mistakes I made, explain why they happened, and show how easy it is to accidentally change behavior when you refactor code. Even with tests in place and decent coverage, assumptions can sneak in, business rules can shift, and logic can quietly break without anyone...
You’ve tested the endpoint. The response looks right. No errors in the terminal. So you’re done, right? Well... not quite. In the last video of this year (time flies!) I start with a tiny FastAPI app that "works", and step by step, I turn it into something that’s actually ready for production (and that's more work than you think). That includes: Proper type usage Input validation and error handling Configuration management Rate limiting to prevent abuse ...and more! All using a real example:...
Sometimes your code fails, you change absolutely nothing, and on the next run everything works again. If that sounds familiar, this week’s video is for you. These kinds of failures usually have nothing to do with bad code. They come from the outside world: APIs that time out, networks that briefly misbehave, or LLMs that occasionally return something almost structured, but not quite. It’s frustrating, because the failure feels random, and those types of failures are really annoying to debug!...