fastcore

Python supercharged for fastai development

fastcore Permissive license Apache-2.0 Active ★ 1,100 v2.2.12 released 2026-08-12

Install

fastcore on PyPI

pip

pip install fastcore

uv

uv add fastcore

poetry

poetry add fastcore

Package facts

License	Apache-2.0 (permissive)
Python support	supports the current Python release (>=3.10)
Install friction	low — pure-Python wheel
Runtime dependencies	none
Maintenance	actively maintained — 1 days since the last release
Last repo commit	2026-08-12
First released	2019-12-02
Popularity	one of the top 1,000 most-downloaded packages on PyPI (30-day window, as of 2026-08-13)
Known vulnerabilities	none known (OSV.dev, checked 2026-08-13)

Evidence: fastcore-2.2.12-py3-none-any.whl

Keywords: python

Development Status :: 5 - Production/StableIntended Audience :: DevelopersNatural Language :: EnglishProgramming Language :: Python :: 3Programming Language :: Python :: 3 :: Only

About fastcore

from the package's own PyPI description — quoted content, verbatim

Welcome to fastcore

> [!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’s starmap, starfilter, and the other star*/rstar* methods are replaced by the star and rstar function adapters, which compose with every L method (e.g. t.map(star(f))); relatedly, spread is replaced by star, and dspread is renamed to dstar. Async helpers now live in the new fastcore.aio module:...

Read as markdown · JSON record · Source repository · Docs

AI interpretation — verify before relying

AI-generated interpretation of the package facts above; every digit, version, license, or vulnerability id it cites is grounded in the facts already shown on this page

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.

Low friction: pure Python wheel with no runtime dependencies, released 1 day ago from an active repository with 1100 stars. Requires Python 3.10+.

Apache-2.0 permissive license allows commercial use, modification, and distribution with minimal restrictions—suitable for most projects.

Usage

pip install fastcore
from fastcore.foundation import L
x = L(1, 2, 3, 4)
result = x.map(lambda o: o * 2)

Requires Python 3.10 or later; fastcore v2 (2.2.12) has breaking changes from v1—pin fastcore<2 if you need old APIs.

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.

Needs verification

Whether the breaking changes in v2 (e.g., Param removal, L method reorganization) affect your existing codebase
Performance characteristics of L vs. native list for your use case

python functional programming utilitiesenhanced list operationsmetaprogramming decoratorsparallel processing helperstesting utilitiespython language extensionsfastai development tools