await input()

Just wanted to share this issue in case someone has ideas.

Problem

With pyolite we can now get a user input with:

i = await input()

which is different than what we are used to in ipython:

i = input()

The fact that we need to await is problematic because it means that wherever this is used, the whole call stack must now be async (you cannot use it in a regular Python function).

Proposed Solution

There is already a running event loop in Jupyterlite, so we can’t just run input until complete. There are two tricks that I know of to work around that, unfortunately they don’t work:

• running input until complete in another thread with its own event loop (pyolite doesn’t support threads).
• using nest-asyncio and run input until complete in the current event loop (nest-asyncio Can't patch loop of type <class 'pyodide.webloop.WebLoop'>).

[joemarshall]

It is possible to do this if you use a service worker. I haven’t done it in my jupyter because I didn’t need it, but I do use a service worker for other things that need to be async in javascript whilst sync in the python webworker.

How it works is the service worker handles fetch requests, which you can trigger from a webworker (like pyolite is) by calling synchronous xmlhttprequest for a special URL that you define. The XMLHttpRequest waits until the fetch responds. So you can call the request, then in the serviceworker fire off whatever async things you want, and only respond to the fetch once that is done.

This can also be done to implement time.sleep without having to use anything clever which is nice.

[alexmojaki]

Just came across someone confused by this now: https://www.reddit.com/r/learnpython/comments/y6jzzd/input_coming_back_as_a_future/

I got here by Googling “jupyterlite input future” but saw several other search results from e.g. StackOverflow from confused people.

In my ideal magical universe there’d be a single piece of code that allowed synchronous communication between kernel and front-end, which would either use service workers, or web threading primitives if they were available because they’re nicer but require server headers.

https://github.com/alexmojaki/sync-message aims to provide this.