serious_python 0.7.0

A cross-platform plugin for adding embedded Python runtime to your Flutter apps.

serious_python

A cross-platform plugin for adding embedded Python runtime to your Flutter apps.

Serious Python embeds Python runtime into a mobile or desktop Flutter app to run a Python program on a background, without blocking UI. Processing files, working with SQLite databases, calling REST APIs, image processing, ML, AI and other heavy lifting tasks can be conveniently done in Python and run directly on a mobile device.

Build app backend service in Python and host it inside a Flutter app. Flutter app is not directly calling Python functions or modules, but instead communicating with Python environmnent via some API provided by a Python program, such as: REST API, sockets, SQLite database or files.

Serious Python is part of Flet project - the fastest way to build Flutter apps in Python. The motivation for building Serious Python was having a re-usable easy-to-use plugin, maintained and supported, to run real-world Python apps, not just "1+2" or "hello world" examples, on iOS or Android devices and hence the name "Serious Python".

Platform Support

iOS	Android	macOS	Linux	Windows
✅	✅	✅	✅	✅

Python versions

• iOS: Python 3.11.6 - based on Kivy toolchain.
• Android: Python 3.11.6 - based on Kivy python-for-android.
• macOS: Python 3.11.6 - based on Beeware's Python Apple Support.
• Linux: Python 3.11.6 - based on indygreg/python-build-standalone.
• Windows: Python 3.11.6 - based on CPython.

Usage

Zip your Python app into app.zip, copy to app (or any other) directory in the root of your Flutter app and add it as an asset to pubspec.yaml:

flutter:
  assets:
    - app/app.zip

Import Serious Python package into your app:

import 'package:serious_python/serious_python.dart';

The plugin is built against iOS 12.0, so you might need to update iOS version in ios/Podfile:

# Uncomment this line to define a global platform for your project
platform :ios, '12.0'

Create an instance of SeriousPython class and call its run() method:

SeriousPython.run("app/app.zip");

When the app starts the archive is unpacked to a temporary directory and Serious Python plugin will try to run main.py in the root of the archive. Current directory is changed to a temporary directory.

If your Python app has a different entry point it could be specified with appFileName parameter:

SeriousPython.run("app/app.zip", appFileName: "my_app.py");

You can pass a map with environment variables that should be available in your Python program:

SeriousPython.run("app/app.zip",
    appFileName: "my_app.py",
    environmentVariables: {"a": "1", "b": "2"});

By default, Serious Python expects Python dependencies installed into __pypackages__ directory in the root of app directory. You can add additional paths to look for 3rd-party packages using modulePaths parameter:

SeriousPython.run("app/app.zip",
    appFileName: "my_app.py",
    modulePaths: ["/absolute/path/to/my/site-packages"]);

Packaging Python app

To simplify the packaging of your Python app Serious Python provides a CLI which can be run with the following command:

dart run serious_python:main

There is package command which takes a directory with Python app as the first argument. The command must be run in Flutter app root directory, where pubspec.yaml is located. The path could be either relative or an absolute.

To package Python files for a mobile app run:

dart run serious_python:main package app/src --mobile

To package for a desktop app run:

dart run serious_python:main package app/src

By default, the command creates app/app.zip asset, but you can change its path/name with --asset argument:

dart run serious_python:main package --asset assets/myapp.zip app/src

If there is requirements.txt or pyproject.toml in the root of source directory package command will try to install dependencies to __pypackages__ in the root of destination archive.

Make sure generated asset is added to pubspec.yaml.

Python app structure

By default, embedded Python program is run in a separate thread, to avoid UI blocking. Your Flutter app is not supposed to directly call Python functions or modules, but instead it should communicate via some API provided by a Python app, such as: REST API, sockets, SQLite database, files, etc.

To constantly run on background a Python program must be blocking, for example a Flask app listening on 8000 port, or you can start your long-running computations in threading.Thread and use threading.Event to prevent program from exiting.

Synchronous execution of Python program is also supported with sync: true parameter to SeriousPython.run() method. For example, it could be a utility program doing some preperations, etc. Just make sure it's either very short or run in a Dart isolate to avoid blocking UI.

Supported Python packages

All "pure" Python packages are supported. These are packages that implemented in Python only, without native extensions written in C, Rust or other low-level language.

For iOS: packages with native extensions having a recipe are supported. To use these packages you need to build a custom Python distributive for iOS (see below).

Platform notes

Build matrix

The following matrix shows which platform you should build on to target specific platforms:

Build on / Target	iOS	Android	macOS	Linux	Windows	Web
macOS	✅	✅	✅			✅
Windows		✅		✅ (WSL)	✅	✅
Linux		✅		✅		✅

macOS

macOS 10.15 (Catalina) is the minimal supported vesion of macOS.

You have to update your Flutter app's macos/Podfile to have this line at the very top:

platform :osx, '10.15'

Also, make sure macos/Runner.xcodeproj/project.pbxproj contains:

MACOSX_DEPLOYMENT_TARGET = 10.15;

Adding custom Python libraries

iOS

serious_python uses Kivy for iOS to build Python and native Python packages for iOS.

Python static library and its dependencies are downloaded and installed during project pod installation from serious_python releases.

To build your own Python distributive with custom native packages and use it with serious_python you need to use toolchain tool provided by Kivy for iOS.

toolchain command-line tool can be run on macOS only.

Start with creating a new Python virtual environment and installing kivy-ios package as described here.

Run toolchain command with the list of packages you need to build, for example to build numpy:

toolchain build numpy

NOTE: The library you want to build with toolchain command should have a recipe in this folder. You can submit a request to make a recipe for the library you need.

You can also install package that don't require compilation with pip:

toolchain pip install flask

This case you don't need to include that package into requirements.txt of your Python app.

When toolchain command is finished you should have everything you need in dist directory.

Get the full path to dist directory by running realpath dist command.

In the terminal where you run flutter commands to build your Flet iOS app run the following command to store dist full path in SERIOUS_PYTHON_IOS_DIST environment variable:

export SERIOUS_PYTHON_IOS_DIST="<full-path-to-dist-directory>"

Clean up old build directory by running:

flutter clean

Build your app by running flutter ios command.

You app's bundle now includes custom Python libraries.

Android

serious_python uses Kivy for Android to build Python and native Python packages for Android.

Python static library and its dependencies are downloaded and installed on pre-build step of Gradle project from serious_python releases.

To build your own Python distributive with custom native packages and use it with serious_python you need to use p4a tool provided by Kivy for Android.

p4a command-line tool can be run on macOS and Linux.

To get Android SDK install Android Studio.

On macOS Android SDK will be located at $HOME/Library/Android/sdk.

Install Temurin8 to get JRE 1.8 required by sdkmanager tool:

brew install --cask temurin8
export JAVA_HOME=/Library/Java/JavaVirtualMachines/temurin-8.jdk/Contents/Home

Set the following environment variables:

export ANDROID_SDK_ROOT="$HOME/Library/Android/sdk"
export NDK_VERSION=25.2.9519653
export SDK_VERSION=android-33

Add path to sdkmanager to PATH:

export PATH=$ANDROID_SDK_ROOT/tools/bin:$PATH

Install Android SDK and NDK from https://developer.android.com/ndk/downloads/ or with Android SDK Manager:

echo "y" | sdkmanager --install "ndk;$NDK_VERSION" --channel=3
echo "y" | sdkmanager --install "platforms;$SDK_VERSION"

Create new Python virtual environment:

python3 -m venv .venv
source .venv/bin/activate

Install p4a:

pip install python-for-android

Install cython:

pip install --upgrade cython

Run p4a with --requirements including your custom Python libraries separated with comma, like numpy in the following example:

p4a create --requirements numpy --arch arm64-v8a --arch armeabi-v7a --arch x86_64 --sdk-dir $ANDROID_SDK_ROOT --ndk-dir $ANDROID_SDK_ROOT/ndk/$NDK_VERSION --dist-name serious_python

Choose No to "Do you want automatically install prerequisite JDK? [y/N]".

NOTE: The library you want to build with p4a command should have a recipe in this folder. You can submit a request to make a recipe for the library you need.

When p4a command completes a Python distributive with your custom libraries will be located at:

$HOME/.python-for-android/dists/serious_python

In the terminal where you run flutter commands to build your Flet Android app run the following command to store distributive full path in SERIOUS_PYTHON_P4A_DIST environment variable:

export SERIOUS_PYTHON_P4A_DIST=$HOME/.python-for-android/dists/serious_python

Clean up old build directory by running:

flutter clean

Build your app by running flutter appbundle command to build .apk.

You app's bundle now includes custom Python libraries.

macOS

List libraries and their versions in requirements.txt in the root of your Python app directory.

Windows

List libraries and their versions in requirements.txt in the root of your Python app directory.

Linux

List libraries and their versions in requirements.txt in the root of your Python app directory.

Troubleshooting

Detailed logging

Use --verbose flag to enabled detailed logging:

dart run serious_python:main package app/src --mobile --verbose

Examples

Python REPL with Flask backend.

Flet app.

Run Python app.