---
title: Foreign Function Interface (FFI)
description: Call JavaScript APIs, bindings, and globals from Python Workers using the Pyodide FFI.
image: https://developers.cloudflare.com/dev-products-preview.png
---

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# Foreign Function Interface (FFI)

Via [Pyodide ↗](https://pyodide.org/en/stable/), Python Workers provide a [Foreign Function Interface (FFI) ↗](https://en.wikipedia.org/wiki/Foreign%5Ffunction%5Finterface) to JavaScript. This allows you to:

* Use [bindings](https://developers.cloudflare.com/workers/runtime-apis/bindings/) to resources on Cloudflare, including [Workers AI](https://developers.cloudflare.com/workers-ai/), [Vectorize](https://developers.cloudflare.com/vectorize/), [R2](https://developers.cloudflare.com/r2/), [KV](https://developers.cloudflare.com/kv/), [D1](https://developers.cloudflare.com/d1/), [Queues](https://developers.cloudflare.com/queues/), [Durable Objects](https://developers.cloudflare.com/durable-objects/), [Service Bindings](https://developers.cloudflare.com/workers/runtime-apis/bindings/service-bindings/) and more.
* Use JavaScript globals, like [Request](https://developers.cloudflare.com/workers/runtime-apis/request/), [Response](https://developers.cloudflare.com/workers/runtime-apis/response/), and [fetch()](https://developers.cloudflare.com/workers/runtime-apis/fetch/).
* Use the full feature set of Cloudflare Workers — if an API is accessible in JavaScript, you can also access it in a Python Worker, writing exclusively Python code.

The details of Pyodide's Foreign Function Interface are documented [here ↗](https://pyodide.org/en/stable/usage/type-conversions.html), and Workers written in Python are able to take full advantage of this.

## Using Bindings from Python Workers

Bindings allow your Worker to interact with resources on the Cloudflare Developer Platform. When you declare a binding on your Worker, you grant it a specific capability, such as being able to read and write files to an [R2](https://developers.cloudflare.com/r2/) bucket.

For example, to access a [KV](https://developers.cloudflare.com/kv) namespace from a Python Worker, you would declare the following in your Worker's [Wrangler configuration file](https://developers.cloudflare.com/workers/wrangler/configuration/):

* [  wrangler.jsonc ](#tab-panel-12138)
* [  wrangler.toml ](#tab-panel-12139)

JSONC

```
{  "main": "./src/index.py",  "kv_namespaces": [    {      "binding": "FOO",      "id": "<YOUR_KV_NAMESPACE_ID>"    }  ]}
```

TOML

```
main = "./src/index.py"
[[kv_namespaces]]binding = "FOO"id = "<YOUR_KV_NAMESPACE_ID>"
```

...and then call `.get()` on the binding object that is exposed on `env`:

Python

```
from workers import WorkerEntrypoint, Response
class Default(WorkerEntrypoint):    async def fetch(self, request):        await self.env.FOO.put("bar", "baz")        bar = await self.env.FOO.get("bar")        return Response(bar) # returns "baz"
```

### Converting Python to JavaScript

Occasionally, to interoperate with JavaScript APIs, you may need to convert a Python object to JavaScript. Pyodide provides a `to_js` function to facilitate this conversion.

Python

```
from js import Objectfrom pyodide.ffi import to_js as _to_js
from workers import WorkerEntrypoint, Response
# to_js converts between Python dictionaries and JavaScript Objectsdef to_js(obj):   return _to_js(obj, dict_converter=Object.fromEntries)
```

For more details, see out the [documentation on pyodide.ffi.to\_js ↗](https://pyodide.org/en/stable/usage/api/python-api/ffi.html#pyodide.ffi.to%5Fjs).

## Using JavaScript globals from Python Workers

We recommend using the `workers` module, which is provided by our `workers-runtime-sdk` package, to access JavaScript globals in a more Pythonic way. However, if you need to access JavaScript globals directly for any reason, you can import them from the `js` module.

For example, note how `Response` is imported from `js` in the example below:

Python

```
from workers import WorkerEntrypointfrom js import Response
class Default(WorkerEntrypoint):    async def fetch(self, request):        return Response.new("Hello World!")
```

Refer to the [Python examples](https://developers.cloudflare.com/workers/languages/python/examples/) to learn how to call into JavaScript functions from Python, including `console.log` and logging, providing options to `Response`, and parsing JSON.

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