Deno Runtime Guide

tywrap's Deno subprocess support is experimental and untested in CI. It uses the same NodeBridge as Node.js, and Deno requires the npm: prefix for npm imports.

Deno Deploy limitation

Deno Deploy does NOT support subprocess execution. Because NodeBridge spawns a Python subprocess, it cannot run in Deno Deploy.

Alternatives for Deno Deploy:

• Use PyodideBridge, which runs Python in-browser via WebAssembly (no subprocess)
• Use HttpBridge, which connects to a remote Python server over HTTP

Installation

deno add npm:tywrap
pip install tywrap-ir

Basic Setup

import { NodeBridge } from 'npm:tywrap';
import { setRuntimeBridge } from 'npm:tywrap/runtime';

setRuntimeBridge(
  new NodeBridge({
    pythonPath: 'python3',
    timeoutMs: 30000,
  })
);

Required Permissions

Deno requires explicit permission flags for subprocess execution:

deno run \
  --allow-run=python3 \
  --allow-read \
  --allow-env \
  your-script.ts

Flag	Reason
--allow-run=python3	Spawn the Python subprocess
--allow-read	Read Python scripts and config files
--allow-env	Read TYWRAP_* and PATH environment variables

Type Checking

deno check src/index.ts

Configuration Options

See the Node.js guide for the full NodeBridgeOptions reference. All options work identically in Deno.

When to Use Each Bridge in Deno

Scenario	Bridge	Notes
Local Deno script	NodeBridge	Needs --allow-run
Deno Deploy	PyodideBridge	WebAssembly, no subprocess
Deno Deploy + heavy Python libs	HttpBridge	Python runs on a separate server

Environment Variables

The same TYWRAP_* env vars work under Deno. See the environment variables reference.

Troubleshooting

PermissionDenied: Requires run access to "python3": add --allow-run=python3 to your deno run command.

NotSupported: Subprocess access is not allowed: you are running in Deno Deploy. Switch to PyodideBridge or HttpBridge.

See the Node.js troubleshooting guide for additional patterns.