A Jupyter-like Python kernel for the browser with real-time streaming output, interrupt support, and seamless visualization capabilities. Run Python code with numpy, matplotlib, plotly, pandas, and more directly in your web applications.

🎯 Features

✅ Real Python Execution - Pyodide-powered Python 3.11 in the browser
✅ Streaming Output - Real-time stdout/stderr streaming as code executes
✅ Interrupt Support - Stop long-running code with SharedArrayBuffer or fallback
✅ Worker Mode - Run Python in Web Workers for better performance
✅ Rich Visualizations - matplotlib, plotly, seaborn plots display automatically
✅ Package Management - Install packages with micropip
✅ TypeScript Support - Full type safety and intellisense
✅ Event System - React to kernel state changes and execution events

🚀 Quick Start

Using CDN (Recommended)

<!DOCTYPE html>
<html>
<head>
    <title>Python in Browser</title>
</head>
<body>
    <div id="output"></div>
    <button id="run">Run Python</button>

    <script type="module">
        // Import from CDN
        import { KernelManager, KernelMode, KernelLanguage } from 'https://cdn.jsdelivr.net/npm/web-python-kernel@0.1.6/dist/web-python-kernel.mjs';
        
        // Create kernel manager with worker mode (recommended)
        const manager = new KernelManager({
            allowedKernelTypes: [
                { mode: KernelMode.WORKER, language: KernelLanguage.PYTHON }
            ],
            // Use SharedArrayBuffer for interrupts if available, fallback to kernel.interrupt()
            interruptionMode: 'auto',
            // Important: specify worker URL when using CDN
            workerUrl: 'https://cdn.jsdelivr.net/npm/web-python-kernel@0.1.6/dist/kernel.worker.js'
        });
        
        // Create a Python kernel
        const kernelId = await manager.createKernel({
            mode: KernelMode.WORKER,
            lang: KernelLanguage.PYTHON
        });
        
        // Execute Python code with real-time streaming
        document.getElementById('run').onclick = async () => {
            const code = `
import matplotlib.pyplot as plt
import numpy as np

print("Generating plot...")
x = np.linspace(0, 10, 100)
y = np.sin(x)
plt.plot(x, y)
plt.title("Sine Wave")
plt.show()
print("Done!")
            `;
            
            // Stream output in real-time
            const stream = manager.executeStream(kernelId, code);
            for await (const event of stream) {
                if (event.type === 'stream' && event.data.name === 'stdout') {
                    document.getElementById('output').innerHTML += event.data.text + '<br>';
                } else if (event.type === 'display_data' && event.data.data['image/png']) {
                    // Display matplotlib plots
                    const img = document.createElement('img');
                    img.src = `data:image/png;base64,${event.data.data['image/png']}`;
                    document.getElementById('output').appendChild(img);
                }
            }
        };
    </script>
</body>
</html>

Alternative CDN URLs

// Latest version
import { KernelManager } from 'https://cdn.jsdelivr.net/npm/web-python-kernel@latest/dist/web-python-kernel.mjs';

// Specific version  
import { KernelManager } from 'https://cdn.jsdelivr.net/npm/web-python-kernel@0.1.6/dist/web-python-kernel.mjs';

// Alternative CDNs
import { KernelManager } from 'https://unpkg.com/web-python-kernel@0.1.6/dist/web-python-kernel.mjs';
import { KernelManager } from 'https://esm.sh/web-python-kernel@0.1.6/dist/web-python-kernel.mjs';

Worker URL Configuration for CDN Usage

When using the library from a CDN, you must specify the full URL to the worker file:

// Using jsdelivr CDN
const manager = new KernelManager({
    workerUrl: 'https://cdn.jsdelivr.net/npm/web-python-kernel@latest/dist/kernel.worker.js'
});

// Using unpkg CDN
const manager = new KernelManager({
    workerUrl: 'https://unpkg.com/web-python-kernel@latest/dist/kernel.worker.js'
});

// For local development (default behavior)
const manager = new KernelManager(); // Will auto-detect worker location

// You can also set it after initialization
manager.setWorkerUrl('https://cdn.jsdelivr.net/npm/web-python-kernel@latest/dist/kernel.worker.js');

Important: When loading from a CDN, always specify the workerUrl to ensure the worker script loads correctly. The library will attempt to auto-detect the worker location, but explicit configuration is more reliable for production use.

NPM Installation

npm install web-python-kernel

import { KernelManager, KernelMode, KernelLanguage, KernelEvents } from 'web-python-kernel';

📋 Basic Usage Example

import { KernelManager, KernelMode, KernelLanguage, KernelEvents } from 'web-python-kernel';

// Create kernel manager
const manager = new KernelManager({
    // Recommend worker mode for better performance and isolation
    allowedKernelTypes: [
        { mode: KernelMode.WORKER, language: KernelLanguage.PYTHON }
    ],
    // Optional: specify worker URL for CDN deployments
    // workerUrl: 'https://cdn.jsdelivr.net/npm/web-python-kernel@latest/dist/kernel.worker.js'
});

// Create a kernel
const kernelId = await manager.createKernel({
    mode: KernelMode.WORKER,
    lang: KernelLanguage.PYTHON
});

// Listen for kernel events
manager.onKernelEvent(kernelId, KernelEvents.KERNEL_BUSY, () => {
    console.log('Kernel is busy...');
});

manager.onKernelEvent(kernelId, KernelEvents.KERNEL_IDLE, () => {
    console.log('Kernel is ready');
});

// Execute Python code with streaming output
const code = `
print("Hello from Python!")
import numpy as np
arr = np.array([1, 2, 3, 4, 5])
print(f"NumPy array: {arr}")
print(f"Sum: {np.sum(arr)}")
`;

// Method 1: Real-time streaming (recommended)
const stream = manager.executeStream(kernelId, code);
for await (const event of stream) {
    switch (event.type) {
        case 'stream':
            if (event.data.name === 'stdout') {
                console.log('Output:', event.data.text);
            }
            break;
        case 'execute_result':
            console.log('Result:', event.data.data['text/plain']);
            break;
        case 'execute_error':
            console.error('Error:', event.data.ename, event.data.evalue);
            break;
    }
}

// Method 2: Simple execution (no streaming)
const kernel = manager.getKernel(kernelId);
const result = await kernel.kernel.execute(code);
if (result.success) {
    console.log('Execution completed');
} else {
    console.error('Execution failed:', result.error);
}

🔧 Worker Mode Setup (Recommended)

Worker mode runs Python in a Web Worker for better performance and isolation:

const manager = new KernelManager({
    allowedKernelTypes: [
        { mode: KernelMode.WORKER, language: KernelLanguage.PYTHON }
    ],
    // Enable SharedArrayBuffer-based interruption (recommended)
    interruptionMode: 'shared-array-buffer'
});

const kernelId = await manager.createKernel({
    mode: KernelMode.WORKER,
    lang: KernelLanguage.PYTHON
});

Interrupt Support with SharedArrayBuffer

For the best interrupt experience, enable SharedArrayBuffer with proper CORS headers:

// Server headers required for SharedArrayBuffer
// Cross-Origin-Opener-Policy: same-origin
// Cross-Origin-Embedder-Policy: require-corp

const manager = new KernelManager({
    // Use 'shared-array-buffer' for best interrupt performance
    // Falls back to 'kernel-interrupt' automatically if SharedArrayBuffer unavailable
    interruptionMode: 'auto' // or 'shared-array-buffer'
});

// Interrupt a long-running execution
const interruptSuccess = await manager.interruptKernel(kernelId);
if (interruptSuccess) {
    console.log('Execution interrupted successfully');
}

🎨 Visualization Support

Web Python Kernel automatically handles matplotlib, plotly, and other visualization libraries:

Matplotlib Example

const matplotlibCode = `
import matplotlib.pyplot as plt
import numpy as np

# Create sample data
x = np.linspace(0, 10, 100)
y = np.sin(x)

# Create plot
plt.figure(figsize=(10, 6))
plt.plot(x, y, label='sin(x)')
plt.plot(x, np.cos(x), label='cos(x)')
plt.title('Trigonometric Functions')
plt.legend()
plt.grid(True)

# Display plot (automatically generates display_data event)
plt.show()
`;

const stream = manager.executeStream(kernelId, matplotlibCode);
for await (const event of stream) {
    if (event.type === 'display_data' && event.data.data['image/png']) {
        // Create img element to display plot
        const img = document.createElement('img');
        img.src = `data:image/png;base64,${event.data.data['image/png']}`;
        img.style.maxWidth = '100%';
        document.body.appendChild(img);
    }
}

Plotly Example

const plotlyCode = `
import micropip
await micropip.install('plotly')
import plotly.graph_objects as go
import numpy as np

# Create interactive plot
x = np.linspace(0, 10, 50)
y = np.sin(x)

fig = go.Figure()
fig.add_trace(go.Scatter(x=x, y=y, mode='lines+markers', name='sin(x)'))
fig.update_layout(title='Interactive Sine Wave')

# Display interactive plot
fig.show()
`;

// Plotly generates HTML display data
const stream = manager.executeStream(kernelId, plotlyCode);
for await (const event of stream) {
    if (event.type === 'display_data' && event.data.data['text/html']) {
        const plotDiv = document.createElement('div');
        plotDiv.innerHTML = event.data.data['text/html'];
        document.body.appendChild(plotDiv);
    }
}

🎮 Try the Interactive Playground

Local Development

# Clone and setup
git clone <repository>
cd web-python-kernel
npm install

# Start playground
npm run playground
# Opens http://localhost:8080/playground.html

Playground Features

✅ Real-time code execution with streaming output
✅ Matplotlib/Plotly visualization examples
✅ Interrupt demonstration for long-running code
✅ Package installation with micropip
✅ Both main thread and worker modes

🔧 Advanced Usage

Kernel Pool Management

Enable kernel pooling for faster kernel creation:

const manager = new KernelManager({
    pool: {
        enabled: true,
        poolSize: 2,              // Keep 2 kernels ready
        autoRefill: true,         // Automatically create new kernels
        preloadConfigs: [
            { mode: KernelMode.WORKER, language: KernelLanguage.PYTHON }
        ]
    }
});

// Pool kernels are created in background, createKernel returns immediately
const kernelId = await manager.createKernel({
    mode: KernelMode.WORKER,
    lang: KernelLanguage.PYTHON
});

// Check pool status
const poolStats = manager.getPoolStats();
console.log('Pool stats:', poolStats);

Multiple Kernels with Namespaces

// Create kernels with namespaces for organization
const dataKernelId = await manager.createKernel({
    namespace: 'data-analysis',
    mode: KernelMode.WORKER,
    lang: KernelLanguage.PYTHON
});

const mlKernelId = await manager.createKernel({
    namespace: 'machine-learning',
    mode: KernelMode.WORKER,
    lang: KernelLanguage.PYTHON
});

// List kernels by namespace
const dataKernels = await manager.listKernels('data-analysis');
console.log('Data analysis kernels:', dataKernels);

// Destroy kernels by namespace
await manager.destroyAll('data-analysis');

Custom Environment Variables

const kernelId = await manager.createKernel({
    mode: KernelMode.WORKER,
    lang: KernelLanguage.PYTHON,
    env: {
        'API_KEY': 'your-api-key',
        'DEBUG': 'true',
        'MODEL_PATH': '/models/trained.pkl'
    }
});

// Python code can access these via os.environ
const code = `
import os
print(f"API Key: {os.environ.get('API_KEY')}")
print(f"Debug mode: {os.environ.get('DEBUG')}")
`;

FileSystem Mounting

const kernelId = await manager.createKernel({
    mode: KernelMode.WORKER,
    lang: KernelLanguage.PYTHON,
    filesystem: {
        mountPoints: {
            '/data': {
                type: 'memory',  // or 'indexeddb'
                initialData: {
                    'dataset.csv': csvData,
                    'config.json': JSON.stringify(config)
                }
            }
        }
    }
});

// Python can now access files
const code = `
import pandas as pd
df = pd.read_csv('/data/dataset.csv')
print(df.head())
`;

Event Handling

import { KernelEvents } from 'web-python-kernel';

// Listen for all kernel events
manager.onKernelEvent(kernelId, KernelEvents.KERNEL_BUSY, () => {
    document.getElementById('status').textContent = 'Running...';
});

manager.onKernelEvent(kernelId, KernelEvents.KERNEL_IDLE, () => {
    document.getElementById('status').textContent = 'Ready';
});

manager.onKernelEvent(kernelId, KernelEvents.STREAM, (data) => {
    if (data.name === 'stdout') {
        appendOutput(data.text);
    } else if (data.name === 'stderr') {
        appendError(data.text);
    }
});

manager.onKernelEvent(kernelId, KernelEvents.DISPLAY_DATA, (data) => {
    if (data.data['image/png']) {
        displayPlot(`data:image/png;base64,${data.data['image/png']}`);
    }
});

manager.onKernelEvent(kernelId, KernelEvents.EXECUTE_ERROR, (data) => {
    showError(`${data.ename}: ${data.evalue}`, data.traceback);
});

Package Installation

// Install packages dynamically
const installCode = `
import micropip
await micropip.install(['pandas', 'scikit-learn', 'seaborn'])

import pandas as pd
import numpy as np
from sklearn.linear_model import LinearRegression
import seaborn as sns

print("All packages installed successfully!")
`;

const stream = manager.executeStream(kernelId, installCode);
for await (const event of stream) {
    if (event.type === 'stream') {
        console.log('Install progress:', event.data.text);
    }
}

Kernel Interruption

// Start a long-running computation
const longCode = `
import time
for i in range(100):
    print(f"Step {i+1}/100")
    time.sleep(1)  # Long-running operation
print("Completed!")
`;

const stream = manager.executeStream(kernelId, longCode);

// Set up interrupt after 5 seconds
setTimeout(async () => {
    const success = await manager.interruptKernel(kernelId);
    if (success) {
        console.log('Execution interrupted successfully');
    }
}, 5000);

// Handle the stream until interruption
try {
    for await (const event of stream) {
        console.log('Output:', event);
    }
} catch (error) {
    if (error.message.includes('interrupt')) {
        console.log('Execution was interrupted');
    }
}

📚 API Reference

KernelManager

class KernelManager {
    constructor(options: IKernelManagerOptions);
    
    // Kernel lifecycle
    createKernel(options: IManagerKernelOptions): Promise<string>;
    getKernel(id: string): IKernelInstance | undefined;
    destroyKernel(id: string): Promise<void>;
    destroyAll(namespace?: string): Promise<void>;
    listKernels(namespace?: string): Promise<KernelInfo[]>;
    
    // Execution
    executeStream(kernelId: string, code: string, parent?: any): AsyncGenerator;
    interruptKernel(kernelId: string): Promise<boolean>;
    
    // Events
    onKernelEvent(kernelId: string, eventType: KernelEvents, listener: Function): void;
    offKernelEvent(kernelId: string, eventType: KernelEvents, listener: Function): void;
    
    // Pool management
    getPoolStats(): Record<string, { available: number; total: number }>;
    getPoolConfig(): PoolConfig;
}

KernelEvents

enum KernelEvents {
    KERNEL_BUSY = 'kernel_busy',
    KERNEL_IDLE = 'kernel_idle',
    STREAM = 'stream',
    DISPLAY_DATA = 'display_data',
    UPDATE_DISPLAY_DATA = 'update_display_data',
    EXECUTE_RESULT = 'execute_result',
    EXECUTE_ERROR = 'execute_error',
    KERNEL_INFO = 'kernel_info'
}

Configuration Options

interface IKernelManagerOptions {
    pool?: IKernelPoolConfig;
    allowedKernelTypes?: Array<{
        mode: KernelMode;
        language: KernelLanguage;
    }>;
    interruptionMode?: 'shared-array-buffer' | 'kernel-interrupt' | 'auto';
}

interface IManagerKernelOptions {
    id?: string;
    mode?: KernelMode;
    lang?: KernelLanguage;
    namespace?: string;
    env?: Record<string, string>;
    filesystem?: IFileSystemMountOptions;
    lockFileURL?: string;
    inactivityTimeout?: number;
    maxExecutionTime?: number;
}

🔍 Performance Tips

Use Worker Mode: Better performance and isolation
Enable Kernel Pooling: Faster kernel creation for frequent use
Use SharedArrayBuffer: Better interrupt performance with proper CORS headers
Preload Packages: Include commonly used packages in lockFileURL
Stream Processing: Use executeStream for real-time feedback

🛡️ Security Considerations

Worker mode provides better isolation than main thread mode
Set appropriate CORS headers for SharedArrayBuffer
Limit allowed kernel types in production
Use namespaces to organize and limit kernel access
Set inactivity timeouts to prevent resource leaks

🛠 Development Commands

Command	Description
`npm run playground`	Build and start playground
`npm run build`	Build kernel bundle
`npm run serve`	Start development server
`npm run test`	Run all tests
`npm run test:watch`	Run tests in watch mode
`npm run clean`	Clean build artifacts

📁 Project Structure

web-python-kernel/
├── src/                    # TypeScript source code
│   ├── manager.ts          # Kernel manager implementation
│   ├── index.ts            # Main kernel implementation
│   ├── types.ts            # TypeScript interfaces
│   └── kernel.worker.ts    # Web Worker implementation
├── tests/                  # Test files
├── playground.html         # Interactive demo
├── dist/                   # Built bundles
│   ├── web-python-kernel.mjs    # ES module
│   ├── web-python-kernel.umd.js # UMD bundle
│   └── kernel.worker.js         # Worker bundle
└── package.json           # Package configuration

🚀 Ready to Go!

Your web-python-kernel is ready to power Jupyter-like Python experiences in the browser!

Quick start: Use the CDN version or install via npm and start building amazing Python web applications.

Happy coding! 🐍✨

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Package last updated on 24 Nov 2025

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