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:
run_sync,
iter_sync, and
ctx_sync moved there
from net, and
maybe_await,
then,
mapa,
acache,
reawaitable,
is_async_callable,
and the other async utilities moved there from xtras.
Config and the config
file functions moved from foundation to xtras. fastcore.net lost
its request builders (urlrequest, urlsend, do_request, urlcheck)
and clean_type_str is gone. parallel_gen moved to fastai. Python
3.11 or later is now required. If you need the old APIs, pin
fastcore<2.
Python is a powerful, dynamic language. Rather than bake everything into
the language, it lets the programmer customize it to make it work for
them. fastcore uses this flexibility to add to Python features
inspired by other languages we’ve loved, mixins from Ruby, and currying,
binding, and more from Haskell. It also adds some “missing features” and
clean up some rough edges in the Python standard library, such as
simplifying parallel processing, and bringing ideas from NumPy over to
Python’s list type.
To install fastcore run: conda install fastcore -c fastai (if you use
Anaconda, which we recommend) or pip install fastcore. For an
editable
install,
clone this repo and run: pip install -e ".[dev]". fastcore is tested
to work on Ubuntu, macOS and Windows (versions tested are those shown
with the -latest suffix
here).
fastcore contains many features, including:
fastcore.test: Simple testing functionsfastcore.foundation: Mixins, delegation, composition, and morefastcore.xtras: Utility functions to help with functional-style programming, parallel processing, and more
To get started, we recommend you read through the fastcore tour.
After you clone this repository, please run nbdev_install_hooks in
your terminal. This sets up git hooks, which clean up the notebooks to
remove the extraneous stuff stored in the notebooks (e.g. which cells
you ran) which causes unnecessary merge conflicts.
To run the tests in parallel, launch nbdev_test.
Before submitting a PR, check that the local library and notebooks match.
- If you made a change to the notebooks in one of the exported cells,
you can export it to the library with
nbdev_prepare. - If you made a change to the library, you can export it back to the
notebooks with
nbdev_update.