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 android.py 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 android.py 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 android.py are:

./android.py configure-build
./android.py make-build
./android.py configure-host HOST
./android.py make-host HOST

HOST identifies which architecture to build. To see the possible values, run ./android.py configure-host --help.

To do all steps in a single command, run:

./android.py 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:

./android.py 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:

./android.py 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

The Python test suite can be run on Linux, macOS, or Windows.

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 suite can usually be run on a device with 2 GB of RAM, but this is borderline, so you may need to increase it to 4 GB. As of Android Studio Koala, 2 GB is the default for all emulators, although the user interface may indicate otherwise. Locate the emulator's directory under ~/.android/avd, and find hw.ramSize in both config.ini and hardware-qemu.ini. Either set these manually to the same value, or use the Android Studio Device Manager, which will update both files.

You can run the test suite either:

Within the CPython repository, after doing a build as described above. 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.
Or by taking a release package built using the package command, extracting it wherever you want, and using its own copy of android.py.

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:
```
./android.py 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:
```
./android.py 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.

Any other arguments on the android.py test command line will be passed through to python -m test – use -- to separate them from android.py'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 android.py 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 android.py make-host or build.

The testbed app can also be used to test third-party packages. For more details, run android.py test --help, paying attention to the options --site-packages, --cwd, -c and -m.

Using in your own app

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

Uh oh!