`asyncio.iscoroutinefunction` is deprecated in Python 3.14, removed in 3.16

[shadowhand]

Summary

fastcore calls asyncio.iscoroutinefunction() in two places. Python 3.14 deprecates it and schedules removal for 3.16, so importing fastcore on 3.14 emits a DeprecationWarning, and on 3.16 these call sites will raise AttributeError.

Reproducing

$ python -c "import fastcore.xtras"
.../fastcore/xtras.py:1239: DeprecationWarning: 'asyncio.iscoroutinefunction'
is deprecated and slated for removal in Python 3.16; use
inspect.iscoroutinefunction() instead
    return async_wrapper if asyncio.iscoroutinefunction(func) else wrapper

The xtras one fires on import, so it surfaces for anyone importing fastcore (or fasthtml) at all — including in test suites that treat warnings as errors.

Call sites

Since these are nbdev-generated, the fix belongs in the notebooks:

Generated	Source
fastcore/xtras.py:1239 (flexicache)	nbs/03_xtras.ipynb
fastcore/parallel.py:162 (parallel_async)	nbs/03a_parallel.ipynb

Both are current as of 2.2.22.

Suggested fix

Swap to inspect.iscoroutinefunction, which CPython names as the replacement. I checked the substitution on 3.14.5 against the shapes these call sites see:

callable	asyncio.	inspect.
async def	True	True
plain def	False	False
functools.partial(async_fn)	True	True
@inspect.markcoroutinefunction	True	True

inspect.iscoroutinefunction has existed since 3.5 and has unwrapped functools.partial since 3.8, so this is safe across the >=3.10 range in settings.ini with no version guard.

One caveat for your judgement: the two differ for callables carrying asyncio's private _is_coroutine marker, which inspect does not consult. That's a private API, so it seems unlikely to matter here, but you'd know better than I would whether anything relies on it.

Environment

fastcore 2.2.13 and 2.2.22 · Python 3.14.5 · macOS and Ubuntu