Python for Android

These instructions are only needed if you're planning to compile Python for Android yourself. Most users should not need to do this. If you're looking to use Python on Android, one of the following tools will provide a much more approachable user experience:

Briefcase, from the BeeWare project
Buildozer, from the Kivy project
Chaquopy

Prerequisites

First, make sure you have all the usual tools and libraries needed to build Python for your development machine.

Second, you'll need an Android SDK. If you already have the 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 also requires the following commands to be on the PATH:

curl
java (or set the JAVA_HOME environment variable)
tar
unzip

Building

Python can be built for Android on any POSIX platform supported by the Android development tools, which currently means Linux or macOS. This involves doing a cross-build where you use a "build" Python (for your development machine) to help produce a "host" Python for Android.

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 an Android build 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

Testing

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

On Linux, the emulator needs access to the KVM virtualization interface, and a DISPLAY environment variable pointing at an X server.
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 directory from somewhere else.

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. The effective setting is hw.ramSize in ~/.android/avd/*.avd/hardware-qemu.ini, whereas Android Studio displays the value from config.ini. Changing the value in Android Studio will update both of these files.

Before running the test suite, follow the instructions in the previous section to build the architecture you want to test. Then run the test script in one of 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.

Uh oh!