Let callback behave like a generator based lifespan function

[NorthLake]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the Typer documentation, with the integrated search.
• I already searched in Google "How to X in Typer" and didn't find any information.
• I already read and followed all the tutorials in the docs and didn't find an answer.
• I already checked if it is not related to Typer but to Click.

Commit to Help

• I commit to help with one of those options 👆

Example Code

import time
from collections.abc import Generator
from concurrent.futures import ThreadPoolExecutor

import typer

app = typer.Typer(no_args_is_help=True, help="A very cool CLI")
UPDATE_CHECK_EXECUTOR = ThreadPoolExecutor(max_workers=1)


def check_for_updates() -> bool:
    time.sleep(2)  # Simulate a delay for checking updates
    return True  # An update is available


@app.callback()
def main() -> Generator[None, None, None]:
    typer.echo("Welcome to the CLI application!")

    update_check_executor = ThreadPoolExecutor(max_workers=1)
    update_check_future = update_check_executor.submit(check_for_updates)

    yield

    if update_check_future.result():
        typer.echo("A new version of the CLI is available. Please update to the latest version")


@app.command()
def run() -> None:
    typer.echo("Running the command...")
    time.sleep(2)  # Simulate some work being done
    typer.echo("Command finished")


if __name__ == "__main__":
    app()

Description

It would be nice if a callback could be interpreted as either a regular function or generator.
If a generator is returned, next would be called after the command has finished. This way some cleanup can be done on a global level, like clearing temporary files.
This would be similar to FastAPI's lifespan feature.

Operating System

Windows

Operating System Details

No response

Typer Version

0.24.1

Python Version

3.13.12

Additional Context

In my case I would use it to do a version check in the background, because it takes a while. I would then display the result at the end after running the command.

[NorthLake]

A non breaking way to implement this would be to check the return type of the callback, and only call next if it's a generator.

[NorthLake]

After some deep diving I discovered that the result_callback argument of the Typer.callback decorator is what I was looking for. Why does the annotation say I shouldn't use this?

[humrochagf]

Did you find a way to have access to the Context in the result_calback?

I was hacking my way around by using click.get_current_context() but now that it got vendored it looks even more hackish by importing it from from typer._click.globals import get_current_context to do the same.

In my use case I make some setup of dependencies using the callback and hooking the initialized dependencies into the context, that then I need to cleanup in the result_callback.

[NorthLake]

Welp, that's what I was using as well. Turns out I hadn't updated typer in a bit. This is quite the bummer.