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Python for Android

If you obtained this README as part of a release package, then the only applicable sections are "Prerequisites", "Testing", and "Using in your own app".

If you obtained this README as part of the CPython source tree, then you can also follow the other sections to compile Python for Android yourself.

However, most app developers should not need to do any of these things manually. Instead, use one of the tools listed here, which will provide a much easier experience.

Prerequisites

If you already have an Android SDK installed, export the ANDROID_HOME environment variable to point at its location. Otherwise, here's how to install it:

  • Download the "Command line tools" from https://developer.android.com/studio.
  • Create a directory android-sdk/cmdline-tools, and unzip the command line tools package into it.
  • Rename android-sdk/cmdline-tools/cmdline-tools to android-sdk/cmdline-tools/latest.
  • export ANDROID_HOME=/path/to/android-sdk

The Platforms/Android script will automatically use the SDK's sdkmanager to install any packages it needs.

The script also requires the following commands to be on the PATH:

  • curl
  • java (or set the JAVA_HOME environment variable)

Building

Python can be built for Android on any POSIX platform supported by the Android development tools, which currently means Linux or macOS.

First we'll make a "build" Python (for your development machine), then use it to help produce a "host" Python for Android. So make sure you have all the usual tools and libraries needed to build Python for your development machine.

The easiest way to do a build is to use the Platforms/Android script. You can either have it perform the entire build process from start to finish in one step, or you can do it in discrete steps that mirror running configure and make for each of the two builds of Python you end up producing.

The discrete steps for building via Platforms/Android are:

python3 Platforms/Android configure-build
python3 Platforms/Android make-build
python3 Platforms/Android configure-host HOST
python3 Platforms/Android make-host HOST

HOST identifies which architecture to build. To see the possible values, run python3 Platforms/Android configure-host --help.

To do all steps in a single command, run:

python3 Platforms/Android build HOST

In the end you should have a build Python in cross-build/build, and a host Python in cross-build/HOST.

You can use -- as a separator for any of the configure-related commands – including build itself – to pass arguments to the underlying configure call. For example, if you want a pydebug build that also caches the results from configure, you can do:

python3 Platforms/Android build HOST -- -C --with-pydebug

Packaging

After building an architecture as described in the section above, you can package it for release with this command:

python3 Platforms/Android package HOST

HOST is defined in the section above.

This will generate a tarball in cross-build/HOST/dist, whose structure is similar to the Android directory of the CPython source tree.

Testing

Tests can be run on Linux, macOS, or Windows, using either an Android emulator or a physical device.

On Linux, the emulator needs access to the KVM virtualization interface. This may require adding your user to a group, or changing your udev rules. On GitHub Actions, the test script will do this automatically using the commands shown here.

The test script supports the following modes:

  • In --connected mode, it runs on a device or emulator you have already connected to the build machine. List the available devices with $ANDROID_HOME/platform-tools/adb devices -l, then pass a device ID to the script like this:

    python3 Platforms/Android test --connected emulator-5554

  • In --managed mode, it uses a temporary headless emulator defined in the managedDevices section of testbed/app/build.gradle.kts. This mode is slower, but more reproducible.

    We currently define two devices: minVersion and maxVersion, corresponding to our minimum and maximum supported Android versions. For example:

    python3 Platforms/Android test --managed maxVersion

By default, the only messages the script will show are Python's own stdout and stderr. Add the -v option to also show Gradle output, and non-Python logcat messages.

Testing Python

You can run the test suite by doing a build as described above, and then running python3 Platforms/Android test. On Windows, you won't be able to do the build on the same machine, so you'll have to copy the cross-build/HOST/prefix directory from somewhere else.

Extra arguments on the Platforms/Android test command line will be passed through to python -m test – use -- to separate them from Platforms/Android's own options. See the Python Developer's Guide for common options – most of them will work on Android, except for those that involve subprocesses, such as -j.

Every time you run python3 Platforms/Android test, changes in pure-Python files in the repository's Lib directory will be picked up immediately. Changes in C files, and architecture-specific files such as sysconfigdata, will not take effect until you re-run python3 Platforms/Android make-host or build.

Testing a third-party package

The Platforms/Android script is also included as android.py in the root of a release package (i.e., the one built using Platforms/Android package).

You can use this script to test third-party packages by taking a release package, extracting it wherever you want, and using the android.py script to run the test suite for your third-party package.

Any argument that can be passed to python3 Platforms/Android test can also be passed to android.py. The following options will be of particular use when configuring the execution of a third-party test suite:

  • --cwd: the directory of content to copy into the testbed app as the working directory.
  • --site-packages: the directory to copy into the testbed app to use as site packages.

Extra arguments on the android.py test command line will be passed through to Python – use -- to separate them from android.py's own options. You must include either a -c or -m argument to specify how the test suite should be started.

For more details, run android.py test --help.

Using in your own app

See https://docs.python.org/3/using/android.html.