# Coming from plain Python

## What is the same

Forge code is Python. An indicator is one file with one class, settings are class attributes, and the work is done in a method that fills arrays. If you can read that, you can read a Forge file.

## What is different

- **The file declares its level.** Every Forge file contains `FORGE_API = 1`. A file without it is refused.
- **Settings are declared, not passed.** `param.Int(14, min=2, max=200)` is a whole number that defaults to 14 and cannot leave 2 to 200. The same declaration builds the settings form and the values a sweep tries.
- **Missing values are NaN.** The first bars of an indicator are empty until it has seen enough bars, and a comparison with `NaN` is false.
- **Decisions are made on closed bars.** A bar that is still forming is not read, and a decision at a bar's close cannot fill at that close.
- **Time is UTC.**

## Where to start

Read three short pages in this order: [repainting and look-ahead](https://oathra.dev/docs/concepts/repainting-and-look-ahead), [warm-up](https://oathra.dev/docs/concepts/warm-up) and [bar close and fills](https://oathra.dev/docs/concepts/bar-close-and-fills). Then write [your first indicator](https://oathra.dev/docs/get-started/draw-your-first-indicator) and [your first strategy](https://oathra.dev/docs/get-started/get-a-verdict).

> **Tip.** Signed in, the assistant on this page ports a snippet for you. Paste it and ask for the Forge version. See [Set up your AI tool](https://oathra.dev/docs/get-started/add-your-ai-tool).