Yeah, "... to run PEXes with." is simply a lie. We were trying to be too helpful with that message but its in the wrong context. We emit it for any search for a Python interpreter whether its to tunr the Pex CLI with, to run a PEX with, or for any other purpose.

later in the logs it seems to be using the correct version of python though 🤔

11:12:03.50 [DEBUG] Completed: Find interpreter for constraints: CPython==3.9.10
11:12:03.50 [DEBUG] Completed: Scheduling: Find interpreter for constraints: CPython==3.9.10
11:12:03.50 [DEBUG] Completed: Find Python interpreter for constraints - Selected /Users/demoda/.pyenv/versions/3.9.10/bin/python3.9 to run PEXes with.
11:12:03.50 [DEBUG] Completed: Hit: Local cache lookup: Determine Python imports for src/hasura_webhooks_proxy/app.py
11:12:03.50 [DEBUG] Completed: Scheduling: Determine Python imports for src/hasura_webhooks_proxy/app.py
11:12:03.51 [DEBUG] Completed: pants.backend.python.util_rules.python_sources.prepare_python_sources
11:12:03.52 [DEBUG] Completed: Hit: Local cache lookup: Building local_dists.pex
11:12:03.52 [DEBUG] Completed: Scheduling: Building local_dists.pex
11:12:03.52 [DEBUG] Completed: pants.backend.python.util_rules.pex.build_pex
11:12:03.52 [DEBUG] Completed: pants.backend.python.util_rules.python_sources.strip_python_sources
11:12:03.52 [DEBUG] Completed: pants.backend.python.util_rules.pex_from_targets.create_pex_from_targets
11:12:03.52 [DEBUG] Completed: Hit: Local cache lookup: Building src.hasura_webhooks_proxy/app.pex with 1 requirement: flask==2.1.1
11:12:03.52 [DEBUG] Completed: Scheduling: Building src.hasura_webhooks_proxy/app.pex with 1 requirement: flask==2.1.1
11:12:03.52 [DEBUG] Completed: pants.backend.python.util_rules.pex.build_pex
11:12:03.52 [DEBUG] Completed: pants.backend.python.goals.package_pex_binary.package_pex_binary
11:12:03.52 [DEBUG] Did not build any upstream Docker images
11:12:03.52 [DEBUG] Built packages for Docker image: src.hasura_webhooks_proxy/app.pex

I should add

linux-x86_64

right?

The easiest way to find out the exact platform string needed is, in your docker image, run this:

/path/to/my/python -mvenv pex.venv
pex.venv/bin/pip install pex
pex.venv/bin/pex --help

In the

pex --help

you're looking for the

--platform

help which will have a line like:

For the current interpreter at /home/jsirois/.venv/pex/bin/python3 the full platform string is manylinux_2_35_x86_64-cp-3.10.2-cp310.

That should save a lot of trouble guessing.

The next problem you can hit is when the resolve for your PEX includes distributions that are only available in source form (.tar.gz or .zip sdist). For that, neither Pants nor Pex offer cross-building; so you must pre-build those wheels. If you hit this problem, I can explain more. Hopefully you don't though.

In our pre-Pants world this is happening with a multi-stage build, which leverages pipenv and a Pipfile to install and build the dependencies. I'd guess I want to do the same thing here, or maybe I need to run Pants inside the container itself as the first stage and not take a dependency on the PEX externally?

From https://www.pantsbuild.org/docs/python-package-goal

PEX files may be platform-specific

If your code's requirements include distributions that include native code, then the resulting PEX file will only run on the platform it was built on.

Yes, unfortunately that is the case for me 😢

One thing to note here. That error you're getting @rapid-exabyte-76685 is very late and it will always happen, even when Linux wheels are available because you have not specified platforms (or, instead

complete_platforms

) for the associated

pex_binary

target. You must use that field to tell Pants to build a multiplatform PEX file that has even a chance of running on Mac and Linux. Once you have platforms specified, the building of the PEX file will fail fast up front if it can't find wheels for every required dependency for each platform you have specified. To get the appropriate platform string for your Docker image, just do something like:

$ docker run --rm python:3.10 bash -c '
> /usr/local/bin/python3.10 -mvenv pex.venv
> pex.venv/bin/pip -q install pex
> pex.venv/bin/pex3 interpreter inspect -v -i2
> '
{
  "path": "/pex.venv/bin/python3.10",
  "version": "3.10.4",
  "requirement": "CPython==3.10.4",
  "platform": "manylinux_2_31_x86_64-cp-3.10.4-cp310",
  "venv": true,
  "base_interpreter": "/usr/local/bin/python3.10"
}

The key thing is to use the full path to the interpreter you want to target in the image in that 1st bash script line.