RuntimeError('There is no current event loop in thread %r.')

[simonw]

https://til.simonwillison.net/ site is down at the moment:

Logs at https://vercel.com/datasette/simon-til/9SYmpgw4ExnTbRLnsevw5zXXTRgb/functions show:

[ERROR] RuntimeError: There is no current event loop in thread 'MainThread'.Traceback (most recent call last): File "/var/task/vc__handler__python.py", line 453, in vc_handler lifespan = Lifespan(__vc_module.app) File "/var/task/vc__handler__python.py", line 308, in __init__ self.loop = get_event_loop() File "/var/task/vc__handler__python.py", line 184, in get_event_loop return asyncio.get_event_loop() File "/var/lang/lib/python3.9/asyncio/events.py", line 642, in get_event_loop raise RuntimeError('There is no current event loop in thread %r.'

[simonw]

This could be a new datasette-publish-vercel bug.

[simonw]

Yup, just deployed https://test-if-vercel-publish-broken.vercel.app/ with this and I'm getting the same error:

datasette publish vercel fixtures.db --project 'test-if-vercel-publish-broken'

[simonw]

I think this is because of changes to Vercel's Python support.

I happened to have a copy of the working vc__handler__python.py from this morning. I generated a new copy using vercel build and here's the diff:

https://gist.github.com/simonw/8521ba3385279fde4a9878f2ad8d150a/revisions

That diff does indeed show newly added code that calls asyncio.get_running_loop():

         def get_event_loop():
            try:
                return asyncio.get_running_loop()
            except:
                if sys.version_info < (3, 10):
                    return asyncio.get_event_loop()
                else:
                    return asyncio.get_event_loop_policy().get_event_loop()

[simonw]

It looks to me like this commit introduced the bug: vercel/vercel@66c8544

It was supposed to fix an issue in Python 3.10. I'm still running Python 3.9 here - so maybe upgrading to Python 3.10 will work around this issue.

[simonw]

The docs at https://vercel.com/docs/runtimes#official-runtimes/python/python-version suggest that you can't run anything other than Python 3.6 or 3.9.

[simonw]

From the PR at https://github.com/vercel/vercel/pull/8045/files it looks like I might be able to use a Pipfile with python_version = "3.10" in it as a workaround.

[simonw]

I tried a manual deploy using the output from --generate-dir

I had to delete requirements.txt - having both that and Pipfile continued to deploy Python 3.9.

This Pipfile:

[[source]]
name = "pypi"
url = "https://pypi.org/simple"
verify_ssl = true

[dev-packages]

[packages]
datasette = '0.61.1'

[requires]
python_version = "3.10"

Seems to have worked in that I'm not getting the old error - I think it deployed Python 3.10 though I've not confirmed it yet, because now I get this error instead:

[ERROR] Runtime.ImportModuleError: Unable to import module 'vc__handler__python': No module named 'datasette'

[simonw]

Alternative workaround, maybe try pinning https://www.npmjs.com/package/@vercel/python to 3.0.7?

[simonw]

Here's how to pin that: https://github.com/vercel-support/flask-test/blob/e8b6f669787c5a7a1343c1e78660ea26407c2a0c/vercel.json#L6

{
  "version": 2,
  "builds": [
    {
      "src": "index.py",
      "use": "@vercel/[email protected]"
    }
  ],
  "routes": [
    {
      "src": "/(.*)",
      "dest": "/"
    }
  ]
}

[simonw]

Yes, this seems to fix it:

        "use": "@vercel/[email protected]"