Python WASM Nodes

Python can run in WASM through several projects, each with trade-offs.

Approaches

Project	Binary Size	Startup	Compatibility
Pyodide	~10 MB	Slow	Full CPython
RustPython	~2 MB	Fast	Most Python
MicroPython	~300 KB	Fast	Subset

Expected Template (Pyodide)

import json

def get_node():
    """Return the node definition."""
    return {
        "name": "wasm_python_uppercase",
        "friendly_name": "Uppercase (Python)",
        "description": "Converts a string to uppercase using Python",
        "category": "Custom/Text",
        "icon": "/flow/icons/text.svg",
        "pins": [
            {
                "name": "exec_in",
                "friendly_name": "▶",
                "description": "Trigger execution",
                "pin_type": "Input",
                "data_type": "Execution",
            },
            {
                "name": "exec_out",
                "friendly_name": "▶",
                "description": "Continue execution",
                "pin_type": "Output",
                "data_type": "Execution",
            },
            {
                "name": "input",
                "friendly_name": "Input",
                "description": "The string to convert",
                "pin_type": "Input",
                "data_type": "String",
                "default_value": "",
            },
            {
                "name": "output",
                "friendly_name": "Output",
                "description": "The uppercase string",
                "pin_type": "Output",
                "data_type": "String",
            },
        ],
        "scores": {
            "privacy": 0,
            "security": 0,
            "performance": 3,  # Python is slower
            "governance": 0,
            "reliability": 0,
            "cost": 1,
        },
    }


def run(context: dict) -> dict:
    """Execute the node logic."""
    input_value = context.get("inputs", {}).get("input", "")

    # Execute logic
    output_value = input_value.upper()

    return {
        "outputs": {
            "output": output_value,
        },
        "error": None,
    }

Why Python in WASM is Challenging

Large runtime — CPython interpreter is ~10MB
Slow startup — Interpreter initialization takes time
Limited I/O — WASM sandbox restricts file/network access
Package compatibility — Not all PyPI packages work in WASM

Recommended Alternatives

For most use cases, consider:

If you need…	Use
Fastest execution	Rust
Familiar syntax	TypeScript
Easy learning curve	Go
Python specifically	Wait for Python support

Current Workaround

You can call Python scripts via the Run Script node in Flow-Like, which executes Python on the host system (not in WASM).

Stay Updated

Python WASM support is on our roadmap. Watch the repository for updates:

📧 [email protected] for enterprise Python node development

→ WASM Nodes Overview → Rust Template → TypeScript Template