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What happens if you try and run that python command?
`python -m pip list -v --format json`

Is there a venv setup for this project? Would be specified in the Pulumi.yaml

I tried pulumi-aws version 4.38.1 (the version it was 4 months back) and also the latest version 5.10.0. I get the same error.

I doubt this is anything to do with the aws version. It a plain python command that's giving a bad exit code.

Pulumi will try to invoke the "right" python based on venv settings, so that might be starting a different python binary to what's the default on your path.

Pipfile reads,

[packages]
pulumi = "&gt;=3.0.0,&lt;4.0.0"
pip = "*"
pulumi-aws = "~=4.38.0"

[requires]
python_version = "3.9"

I tried changing the Pipfile to show python 3.9, 3.8 and 3.10. Maybe there is a mismatch between python version and pulumi-aws version.

Can you run with --logtostderr -v5 and see what that prints. It should include a line like `Language host launching process` which will say exactly what python is being run

It threw a lot of info. There was no `Language host launching process`

Oh sorry my bad, of course that message comes from the language plugin so it needs `--logflow` added to the command to show up :man-facepalming:  sorry

The output showed a venv path to python. I checked the python version. It is Python 3.10.5. Not the intended 3.9 as shown in Pipfile.

And if you run `-m pip list -v` with that python does it error?

The path also contains python3.9 along with python(which is 3.10). How can I make pulumi use python3.9 ?

I think it's hardcoded to use an executable called "python", doesn't look like there's anyway to override that currently.

Annoyingly the env var PULUMI_PYTHON_CMD can change it, but it doesn't get picked up when on the venv path. Which arguably is a bug.

I deleted the "python" in the venv. Then recreated the "python" as a soft link to /usr/bin/python3.9. The error is gone. Thank you Fraser.

A recent update of python from 3.9 to 3.10 has caused the issue in some old pulumi projects.

FYI I've also raised <https://github.com/pulumi/pulumi/pull/10155> to allow overriding of this via envvar in the future