Chapter 0: Python WebAssembly Terminal

Welcome to the Python WebAssembly (WASM) terminal! This chapter provides a fully interactive Python REPL (Read-Eval-Print Loop) running entirely in your browser, powered by Pyodide.

Interactive Python REPL

Quick Start Guide

The terminal above is a fully functional Python environment. Try these commands:

Terminal Features

Available Libraries

• Click - Pre-installed and ready to use
• Standard Library - Full Python 3.11 standard library
• File System - Virtual file system at /tmp
• Subprocess - Simulated subprocess for testing

Keyboard Shortcuts

• Enter: Execute single-line commands
• Shift+Enter: Insert newline (for multi-line code)
• Up/Down Arrow: Navigate command history
• Tab: Auto-completion (where available)
• Ctrl+C: Interrupt execution
• Ctrl+L: Clear terminal

Special Commands

• help(): Python help system
• dir(): List available objects
• globals(): Show global namespace
• %clear: Clear terminal output
• %reset: Reset Python environment

Comprehensive Test Suite

Copy and paste these test blocks into the REPL to verify functionality:

Test 1: Environment Verification

Test 2: Click Framework Testing

Test 3: Advanced Click Features

Test 4: File System Operations

Test 5: Error Handling and Exceptions

Test 6: Progress Bars and Styling

Test 7: Complex CLI Application

Tips for Using the REPL

1. Multi-line Input: Use Shift+Enter to write multi-line code blocks
2. Interrupting: Use Ctrl+C to interrupt long-running code
3. Click Testing: Always use CliRunner for testing Click commands in the REPL
4. File Paths: Use /tmp for temporary file operations
5. Async Code: Pyodide supports async/await - try await fetch() for web requests

Troubleshooting

Common Issues

1. SystemExit Errors: Click commands call sys.exit() by default. Always use CliRunner for testing.
2. Import Errors: Some packages may not be available. Use micropip to install additional packages.
3. Memory Limits: The browser environment has memory constraints. Avoid very large data operations.

Installing Additional Packages

Note: To install additional packages in the REPL above, use:

import micropip
await micropip.install('requests')

For interactive code blocks, packages must be pre-configured. Click is already pre-loaded!

Mobile Support

This REPL is fully functional on mobile devices:

• Touch to focus: Tap the terminal to bring up the keyboard
• Pinch to zoom: Zoom in/out for better visibility
• Landscape mode: Rotate for more screen space

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Ready to explore? Start typing Python code in the terminal above!

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