Flit-core

3.12.0 · active · verified Sun Mar 29

Flit-core provides a PEP 517 compliant build backend, encapsulating the core distribution-building logic for projects that use Flit for packaging. It is an essential dependency for the user-facing `flit` tool, enabling the creation of wheels and source distributions. The current version is 3.12.0, released on March 25, 2025, and maintains a fairly active release cadence with multiple updates throughout the year.

Warnings

breaking Upcoming Flit 4.0 (which uses flit-core) plans to remove support for old-style metadata in `[tool.flit.metadata]` in favor of the standardized `[project]` table in `pyproject.toml`.
Fix: Migrate your project's metadata from `[tool.flit.metadata]` to the `[project]` table in `pyproject.toml`.
breaking In Flit 4.0, the `flit build` command will no longer default to using information from Git to determine source distribution contents. This changes how `sdist` includes are determined by default, to be more explicit.
Fix: Explicitly define `sdist` inclusions/exclusions in `pyproject.toml` under `[tool.flit.sdist]`, or use `python -m build` which already bypasses this implicit Git integration.
gotcha Flit-core provides a PEP 517 build backend and is an internal component. Direct programmatic interaction for general packaging tasks is usually done via the `flit` CLI or standard tools like `python -m build` and `twine`.
Fix: For packaging projects, install `flit` (`pip install flit`) and use its CLI commands (`flit init`, `flit build`, `flit publish`), or use `python -m build` combined with `twine upload` for a more universal packaging workflow.
gotcha Flit-core requires Python 3. While older `flit-core` versions supported Python 3.4+, current versions (like 3.12.0) explicitly require `Python >=3.6`. Ensure your environment meets this minimum requirement.
Fix: Ensure your development and build environments use Python 3.6 or newer.

Install

pip install flit-core Install flit-core

Imports

buildapi
```
from flit_core import buildapi
```
flit_core.buildapi is the *only* public interface, exposed for PEP 517 build backend integration. Direct user-level imports for typical application logic are uncommon; most users interact via the `flit` CLI or `python -m build`.

Quickstart

Flit-core is a build backend, not typically imported directly by end-user applications for their runtime logic. Its primary 'usage' is being declared in a project's `pyproject.toml` file to specify how the package should be built. The example shows the standard `pyproject.toml` configuration for using `flit-core`.

# This is typically found in pyproject.toml, not direct Python code.
# A project using flit-core as its build backend would declare it like this:

# pyproject.toml
# [build-system]
# requires = ["flit_core>=3.2,<4"]
# build-backend = "flit_core.buildapi"

print("flit-core is primarily a build backend. ")
print("Its usage is declared in pyproject.toml and invoked by build tools.")
print("For creating and publishing a package, install 'flit' (pip install flit).")
print("Then run 'flit init' and 'flit publish'.")

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