Chat's .append_message_stream() now returns an ExtendedTask

[cpsievert]

This PR does 2 things:

• Adds new get_latest_stream_result() method for an easy way to access the final result of the stream when it completes.
• The .append_message_stream() method now returns the reactive.extended_task instance that it launches.

import asyncio

from shiny.express import render, ui

chat = ui.Chat("chat")

chat.ui()
chat.update_user_input(value="Press Enter to start the stream")


async def stream_generator():
    for i in range(10):
        await asyncio.sleep(0.25)
        yield f"Message {i} \n\n"


@chat.on_user_submit
async def _(message: str):
    await chat.append_message_stream(stream_generator())


@render.code
async def stream_result_ui():
    return chat.get_latest_stream_result()

chat-stream-result.mp4

TODO

• Add return section to docstring?

[gadenbuie]

@chat.on_user_submit
async def _(message: str):
    stream = await chat.append_message_stream(stream_generator())
    current_stream.set(stream)


current_stream: reactive.value[ExtendedTask[[], str] | None] = reactive.value(None)

Could we wrap this bit up in a method, e.g. chat.get_last_stream() (naming is hard)? That might be technically difficult, but I think this pattern would be hard for users to "discover" on their own.

[cpsievert]

Could we wrap this bit up in a method

I went back and forth a bit on whether I wanted to add this since shinychat won't be able have an equivalent, but I think the end result (f625eba) is worth it.

Note that I also decided to get the result of the stream, not the stream itself since >95% of the time you just want the result.

[gadenbuie]

Looks great! I like the method interface 😄