ViaPyodide ↗, Python Workers provide aForeign Function Interface (FFI) ↗ to JavaScript. This allows you to:

• Usebindings to resources on Cloudflare, includingWorkers AI,Vectorize,R2,KV,D1,Queues,Durable Objects,Service Bindings and more.
• Use JavaScript globals, likeRequest,Response, andfetch().
• 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 documentedhere ↗, and Workers written in Python are able to take full advantage of this.

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 anR2 bucket.

For example, to access aKV namespace from a Python Worker, you would declare the following in your Worker'sWrangler configuration file:

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

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

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

from workersimport WorkerEntrypoint, Response
classDefault(WorkerEntrypoint):
asyncdeffetch(self,request):
awaitself.env.FOO.put("bar","baz")
bar=awaitself.env.FOO.get("bar")
returnResponse(bar)# returns "baz"

Under the hood,env is actually a JavaScript object. When you call.FOO, you are accessing this property via aJsProxy ↗ — special proxy object that makes a JavaScript object behave like a Python object.

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

from jsimport Object
from pyodide.ffiimport to_jsas _to_js
from workersimport WorkerEntrypoint, Response
# to_js converts between Python dictionaries and JavaScript Objects
defto_js(obj):
return_to_js(obj,dict_converter=Object.fromEntries)
```

For more details, see out thedocumentation onpyodide.ffi.to_js ↗.

When writing Workers in Python, you can access JavaScript globals by importing them from thejs module. For example, note howResponse is imported fromjs in the example below:

from workersimport WorkerEntrypoint
from jsimport Response
classDefault(WorkerEntrypoint):
asyncdeffetch(self,request):
return Response.new("Hello World!")

Refer to thePython examples to learn how to call into JavaScript functions from Python, includingconsole.log and logging, providing options toResponse, and parsing JSON.