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 multi-platform 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

• Python 3.12.6 on all platforms.

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 the specific platform:

dart run serious_python:main package app/src -p {platform}

where {platform} can be one of the following: Android, iOS, macOS, Windows, Linux or Pyodide.

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 -p {platform}

Python app dependencies can be installed with --requirements option. The value of --requirements option is passed "as is" to pip command. For example, --requirements flet,numpy==2.1.1 will install two requirements directly, or --requirements -r,requirements.txt installs deps from requirements.txt file.

To package for iOS and Android platforms developer should set SERIOUS_PYTHON_SITE_PACKAGES environment variable with a path to a temp directory for installed app packages. The contents of that directory is embedded into app bundle during app compilation.

For example:

export SERIOUS_PYTHON_SITE_PACKAGES=$(pwd)/build/site-packages
dart run serious_python:main package app/src -p iOS --requirements -r,app/src/requirements.txt

For macOS, Linux and Windows app packages are installed into __pypackages__ inside app package asset zip.

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.

The following iOS and Android packages are supported: https://pypi.flet.dev

The following Pyodide packages are supported: https://pyodide.org/en/stable/usage/packages-in-pyodide.html

Additional Python binary packages for iOS and Android can be built with adding a new recipe to Mobile Forge project.

Request additional packages for iOS and Android on Flet Discussions - Packages.

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;

Android

To make serious_python work in your own Android app:

If you build an App Bundle Edit android/gradle.properties and add the flag:

android.bundle.enableUncompressedNativeLibs=false

If you build an APK Make sure android/app/src/AndroidManifest.xml has android:extractNativeLibs="true" in the <application> tag.

For more information, see the public issue.

Troubleshooting

Detailed logging

Use --verbose flag to enabled detailed logging:

dart run serious_python:main package app/src -p Darwin --verbose

Examples

Python REPL with Flask backend.

Flet app.

Run Python app.