Brython Runner

A JavaScript library that runs Python 3 code on web browsers based on Brython.

Brython is designed to replace JavaScript in the Web; it allows you to use Python 3 instead of JavaScript as the scripting language for your web application. Brython does that by translating Python code into the equivalent JavaScript code.

However, if you want to run user-written Python code in your web application, it's not so simple to do so. Use Brython Runner for that.

Demo

See how Pythonpad runs user-written Python 3 code on the browser with Brython Runner; it supports input(), time.sleep(x), and file system with local .py import feature.

If you need a simple example, see our demo page and see brython-runner in action.

Installation

Node.js

$ npm install brython-runner

Usage

Browser

The simple way to use it in a browser:

<script src="lib/brython-runner.bundle.js"></script>
<script>
    async function runPythonCode() {
        const runner = new BrythonRunner({
            stdout: {
                write(content) {
                    console.log('StdOut: ' + content);
                },
                flush() {},
            },
            stderr: {
                write(content) {
                    console.error('StdErr: ' + content);
                },
                flush() {},
            },
            stdin: {
                async readline() {
                    var userInput = prompt();
                    console.log('Received StdIn: ' + userInput);
                    return userInput;
                },
            }
        });
        console.log('Run Code:');
        await runner.runCode('print("hello world")\nprint("from Brython Runner")');
        console.log('Done.');
    }
    runPythonCode();
</script>

Webpack

You can directly require the module if you're using webpack to bundle your project. For example:

var BrythonRunner = require('brython-runner/lib/brython-runner.js').default;

or with import syntax:

import BrythonRunner from 'brython-runner/lib/brython-runner.js';

Note

The core source of BrythonRunner uses raw-loader for importing JavaScript and Python scripts as String values. If your working in non-webpack CommonJS environment, be sure to handle import statements with prefix !!raw-loader! in the source. For example:

import stdioSrc from '!!raw-loader!../scripts/stdio.py'
import sleepSrc from '!!raw-loader!../scripts/sleep.py'
import fileioSrc from '!!raw-loader!../scripts/fileio.py'

Usage Examples

Simple

const runner = new BrythonRunner({
    stdout: {
        write(content) {
            console.log('StdOut: ' + content);
        },
        flush() {},
    },
    stderr: {
        write(content) {
            console.error('StdErr: ' + content);
        },
        flush() {},
    },
    stdin: {
        async readline() {
            var userInput = prompt();
            console.log('Received StdIn: ' + userInput);
            return userInput;
        },
    }
});
await runner.runCode('print("hello world")');

Debug Level

Set debug option to explicitly set the debug level for Brython. See this page from the Brython website for more information.

• 0 (default) : no debugging. Use this when the application is debugged, it slightly speeds up execution
• 1 : error messages are printed in the browser console (or to the output stream specified by sys.stderr)
• 2 : the translation of Python code into Javascript code is printed in the console
• 10 : the translation of Python code and of the imported modules is printed in the console

const runner = new BrythonRunner({ debug: 10 });

Init Callback

Use onInit option to set a function that is called after the web worker initialization.

const runner = new BrythonRunner({
    onInit() {
        console.log('Runner web worker is ready!');
    },
});

Standard Input

Brython Runner requires a hanger server to support Python's input() function in the web worker environment.

A Brython Runner instance will use the hanger server instance served for the Pythonpad service on default settings. However, you can serve your own hanger server and provide the URL to the server as hangerUrl option.

const runner = new BrythonRunner({
    hangerUrl: 'https://www.pythonpad.co/hanger',
});

An aiohttp-based implementation of a hanger server is available in this repository: Brython Runner StdIn Hanger. Go check out detailed information on how standard input works in the Brython Runner.

Files

Use runCodeWithFiles method with onFileUpdate option to provide files and directories for the Python code.

const files = {
    'hello.py': {
        'type': 'text',
        'body': 'print("hello world")',
    },
    'data/': {
        'type': 'dir',
        'body': '',
    },
    'data/image.gif': {
        'type': 'base64',
        'body': 'R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7',
    },
    'main.py': {
        'type': 'text',
        'body': 'import hello\nf = open("data/image.gif", "rb")\nf.close()',
    }
};
const runner = new BrythonRunner({
    onFileUpdate(filename, data) {
        files[filename].type = data.type;
        files[filename].body = data.body;
    },
});
runner.runCodeWithFiles(files['main.py'].body, files);

BrythonRunner.runCodeWithFiles(code, files) method runs Python code with given files. Files must be provided as a JavaScript object that contains each file or directory as a key-value pair.

An object key for a file or a folder represents a path to the file from a virtual current working directory. A path for a file should be normalized (os.path.normpath(path) === path) and should be inside the current working directory (e.g., ../file.txt is not allowed). If a path is for a folder, it should have a trailing slash added to a normalized path. See the data/ folder in the example code.

A value for a file or a folder should be a JavaScript object that contains values for the keys: type and body. If it is a folder, type should be 'dir' and body should be an empty string (''). If it is a file, two types are available: 'text' and 'base64'.

Files with 'text' type should have string type content of the file as the body value. Files with 'base64' type should have the content encoded in base64 as the body value.

If the files are edited while running the code, a function given as onFileUpdate option is called. The path of the edited file is given as the first parameter (filename) and the data object with type and body values is given as the second parameter (data).

Development

To serve the exmaple web page for development, run:

$ npm dev

Check out http://localhost:4000 on your web browser to see the example web page.

To build the library, run:

$ npm build