Mar 24, 2026

Here’s how I like to structure application’s entry point (aka main()).

1. It’s responsibility is to provide CLI interface to the library.

2. It parses CLI arguments, loads configuration files, constructs the processing pipeline and kicks it off.

3. Each step might be extracted into a separate function/class/module as it grows in complexity.

4. One common pattern is to construct intermiate immutable configuration object from arguments and configuration files and pass down to a dedicated factory. This way factory is easy to reuse and test without working around arguments parsing. On the cons side, each parameter spreads over three places: CLI, intermediate config, actor constructor.

5. The same patterns works well for both local scripts and API services.

This is mostly common sense, and I’ve seen more specific and more generic versions of this design many times. I never meant to write it down, as there’s no novelty in clean code layout, until I made a habbit of explaining this to LLMs over and over.