Android: site-packages ship zipped; some packages need `extract_packages`

:::note This guide is accurate as of Flet 0.86.0. Later releases might add new APIs or additional migration paths.

The breaking changes and deprecations index lists the guides created for each release. :::

Summary

Flet 0.86.0 changes how Python code is packaged into Android apps (flet build apk / aab):

Native extension modules (.so files) are loaded memory-mapped directly from the APK — no extraction to disk.
Pure Python code — the standard library and your site-packages — ships in stored zip assets (stdlib.zip, sitepackages.zip) and is imported in place via zipimport, so it is no longer duplicated per ABI or unpacked on first launch.

This makes APKs significantly smaller and removes the need for useLegacyPackaging / keepDebugSymbols workarounds. Importing from a zip is transparent to most packages.

Some packages still locate bundled data files through a real filesystem path, usually with __file__ or pkg_resources, instead of the zip-safe importlib.resources. Those packages must be listed in extract_packages so they ship extracted to disk.

This affects Android only. On macOS, iOS, Windows, and Linux, site-packages ship unpacked; web (Pyodide) is unchanged.

For the maintained feature documentation, including examples, wildcard behavior, and the current list of known affected packages, see Android packaging: extract packages.

Symptoms

The build succeeds, but the app crashes or errors on the device when the package is imported or first used. The traceback usually contains a path where sitepackages.zip or stdlib.zip appears as a directory component, for example:

bash

FileNotFoundError: [Errno 2] No such file or directory:
  '/data/user/0/<applicationId>/files/.../sitepackages.zip/matplotlib/mpl-data/matplotlibrc'

NotADirectoryError or OSError with a similar sitepackages.zip/... path is also a common sign that the package computed a data path from __file__ and tried to read it as a regular file.

Migration guide

Add the failing package's import name to your pyproject.toml:

toml

[tool.flet.android]
extract_packages = ["matplotlib", "sklearn"]

or pass them on the command line:

bash

flet build apk --android-extract-packages matplotlib sklearn

An entry is the package's import name — its top-level directory under site-packages — not the PyPI distribution name: sklearn, not scikit-learn; cv2, not opencv-python.

Flet extracts the listed package directories and everything under them to the app's files directory, so __file__-relative reads work again.

No action needed for

Apps targeting only desktop, iOS, or web.
Android apps whose dependencies are all zip-safe (the common case) — the change is then purely a size win.

Timeline

Changed in: 0.86.0

Android: site-packages ship zipped; some packages need extract_packages