Async support

[tiangolo]

Privileged issue

• I'm @tiangolo or he asked me directly to create an issue here.

Issue Content

I want Typer to have optional support for async functions.

It would depend on having AnyIO (or maybe Asyncer 🤔) installed. If the command function is async, then it would run it with anyio.run().

Maybe autocompletion functions could also be async, so they would have to be checked to see if they need to be called directly or awaited.

[gaby]

Why not use native asyncio.run() ?

[Deltik]

I'm currently using this type-annotated wrapper to make the Typer.callback() and Typer.command() decorators compatible with both async and non-async functions:

import asyncio
import inspect
from collections.abc import Callable, Coroutine
from functools import wraps
from typing import Any, ParamSpec, TypeVar, cast

from typer import Typer
from typer.core import TyperCommand, TyperGroup
from typer.models import CommandFunctionType

P = ParamSpec("P")
R = TypeVar("R")


class AsyncTyper(Typer):
    @staticmethod
    def maybe_run_async(
        decorator: Callable[[CommandFunctionType], CommandFunctionType],
        f: CommandFunctionType,
    ) -> CommandFunctionType:
        if inspect.iscoroutinefunction(f):

            @wraps(f)
            def runner(*args: Any, **kwargs: Any) -> Any:
                return asyncio.run(cast(Callable[..., Coroutine[Any, Any, Any]], f)(*args, **kwargs))

            return decorator(cast(CommandFunctionType, runner))
        return decorator(f)

    # noinspection PyShadowingBuiltins
    def callback(
        self,
        name: str | None = None,
        *,
        cls: type[TyperGroup] | None = None,
        invoke_without_command: bool = False,
        no_args_is_help: bool = False,
        subcommand_metavar: str | None = None,
        chain: bool = False,
        result_callback: Callable[..., Any] | None = None,
        context_settings: dict[Any, Any] | None = None,
        help: str | None = None,  # noqa: A002
        epilog: str | None = None,
        short_help: str | None = None,
        options_metavar: str = "[OPTIONS]",
        add_help_option: bool = True,
        hidden: bool = False,
        deprecated: bool = False,
        rich_help_panel: str | None = None,
    ) -> Callable[[CommandFunctionType], CommandFunctionType]:
        decorator = super().callback(
            name=name,
            cls=cls,
            invoke_without_command=invoke_without_command,
            no_args_is_help=no_args_is_help,
            subcommand_metavar=subcommand_metavar,
            chain=chain,
            result_callback=result_callback,
            context_settings=context_settings,
            help=help,
            epilog=epilog,
            short_help=short_help,
            options_metavar=options_metavar,
            add_help_option=add_help_option,
            hidden=hidden,
            deprecated=deprecated,
            rich_help_panel=rich_help_panel,
        )
        return lambda f: self.maybe_run_async(decorator, f)

    # noinspection PyShadowingBuiltins
    def command(
        self,
        name: str | None = None,
        *,
        cls: type[TyperCommand] | None = None,
        context_settings: dict[Any, Any] | None = None,
        help: str | None = None,  # noqa: A002
        epilog: str | None = None,
        short_help: str | None = None,
        options_metavar: str = "[OPTIONS]",
        add_help_option: bool = True,
        no_args_is_help: bool = False,
        hidden: bool = False,
        deprecated: bool = False,
        rich_help_panel: str | None = None,
    ) -> Callable[[CommandFunctionType], CommandFunctionType]:
        decorator = super().command(
            name=name,
            cls=cls,
            context_settings=context_settings,
            help=help,
            epilog=epilog,
            short_help=short_help,
            options_metavar=options_metavar,
            add_help_option=add_help_option,
            no_args_is_help=no_args_is_help,
            hidden=hidden,
            deprecated=deprecated,
            rich_help_panel=rich_help_panel,
        )
        return lambda f: self.maybe_run_async(decorator, f)

There is no dependency on AnyIO or Asyncer.

[albireox]

This would be a useful addition. Currently I'm using a decorator to run the async callback

def cli_coro(
    signals=(signal.SIGHUP, signal.SIGTERM, signal.SIGINT),
    shutdown_func=None,
):
    """Decorator function that allows defining coroutines with click."""

    def decorator_cli_coro(f):
        @wraps(f)
        def wrapper(*args, **kwargs):
            loop = asyncio.get_event_loop()
            if shutdown_func:
                for ss in signals:
                    loop.add_signal_handler(ss, shutdown_func, ss, loop)
            return loop.run_until_complete(f(*args, **kwargs))

        return wrapper

    return decorator_cli_coro

@cli_coro()
async def cli_command(...):

but it would be useful to have an option directly in Typer.

[bckohan]

Strong support for async! Especially for chained sub commands.

I'm not sure it makes sense to support async shell completions though. There's never an instance where more than one parameter needs completion simultaneously and if you need to do multiple I/O bound things at once to complete a parameter you can just start an event loop in your completer function.