dart_monty_wasm

Part of dart_monty — pure Dart bindings for Monty, a restricted, sandboxed Python interpreter built in Rust.

Live Demo | GitHub | Monty

This package is co-designed by human and AI — nearly all code is AI-generated.

Pure Dart web WASM implementation of dart_monty using dart:js_interop and @pydantic/monty. Runs the Monty Python interpreter in a Web Worker to avoid Chrome's synchronous WASM compile-size limit.

This package has no Flutter dependency and can be used in any Dart web project.

• Flutter apps should import dart_monty instead — the federated plugin selects the correct backend automatically.
• Pure Dart web projects can depend on this package directly to run Python via WASM in the browser.

Architecture

Dart (compiled to JS) -> MontyWasm (dart:js_interop)
  -> DartMontyBridge (monty_glue.js)
    -> Web Worker (dart_monty_worker.js)
      -> @pydantic/monty WASM (NAPI-RS)

Key Classes

Multi-Session Worker Pool (0.7.0)

Each session runs in its own Worker with isolated memory. NAPI-RS overhead has been stripped (asyncWorkPoolSize: 0, shared: false), reducing memory from 256 MB to 16 MB per session. Snapshots transfer as Uint8Array (binary, no JSON serialization). Cancellation calls Worker.terminate() for preemptive kill with full crash isolation.

Requirements

The web server must send COOP/COEP headers for SharedArrayBuffer support:

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

Usage

import 'package:dart_monty_wasm/dart_monty_wasm.dart';

Future<void> main() async {
  final monty = MontyWasm(bindings: WasmBindingsJs());

  final result = await monty.run('2 + 2');
  print(result.value); // 4

  await monty.dispose();
}

See the main dart_monty repository for full documentation.