---
id: fastcore
version: "2.2.12"
license: Apache-2.0
license_treatment: permissive
maintenance: active
---

# fastcore — Python supercharged for fastai development

License: permissive · Maintenance: active · Popularity: top 1,000 on PyPI

## Install

pip install fastcore
uv add fastcore
poetry add fastcore

## Description

# Welcome to fastcore


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> [!NOTE]
>
> ### fastcore v2
>
> In July 2026 we released fastcore v2, which removes or relocates a number of APIs that had accumulated better alternatives. If you use `from fastcore.utils import *` (or `fastcore.all`), most of these changes won’t affect you. The breaking changes: `Param` is gone from `fastcore.script`; use plain type annotations with docments, or `typing.Annotated[type, "help"]`, optionally with a `dict` of argparse arguments for advanced features. [`L`](https://fastcore.fast.ai/foundation.html#l)’s `starmap`, `starfilter`, and the other `star*`/`rstar*` methods are replaced by the [`star`](https://fastcore.fast.ai/foundation.html#star) and [`rstar`](https://fastcore.fast.ai/foundation.html#rstar) function adapters, which compose with every [`L`](https://fastcore.fast.ai/foundation.html#l) method (e.g. `t.map(star(f))`); relatedly, `spread` is replaced by [`star`](https://fastcore.fast.ai/foundation.html#star), and `dspread` is renamed to [`dstar`](https://fastcore.fast.ai/basics.html#dstar). Async helpers now live in the new `fastcore.aio` module:...

## AI interpretation — verify before relying

fastcore extends Python with functional programming tools, enhanced list operations via the L type, decorators for metaprogramming (@patch, @delegates), parallel execution helpers, and utilities for testing, file I/O, and CLI creation.

Verdict: fastcore is a stable, actively maintained library (last release 1 day ago, 1100 GitHub stars) offering Pythonic extensions for functional programming and metaprogramming. Zero security vulnerabilities, no dependencies, and permissive licensing make it low-risk. The v2 API restructuring is documented; users upgrading should review the migration notes.

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