TL;DR: polars is not installed in the environment running your code. Run `pip install polars` (in the right environment) and the import works.

## The error
```text
ModuleNotFoundError: No module named 'polars'
```

## Fix it
1. Confirm which python runs your code:
   ```
   which python && python --version
   ```
   Expected: shows the interpreter you mean to use.
2. Install polars into it:
   ```
   python -m pip install polars
   ```
   Expected: install completes.
3. Verify:
   ```
   python -c "import polars; print(polars.__version__)"
   ```
   Expected: prints the version.
4. In CI, add polars to the requirements file so the next run does not regress.

## When this applies
Use this when `import polars` raises the missing-module error, especially in CI or fresh containers.

## When it does not apply
If polars is installed but the import still fails, you are in the wrong environment; check which pip and which python. If the error is a different message, that is a separate issue.

## Compatibility
All polars versions; wheels exist for major platforms and Python versions.

## Root cause
The code runs under an interpreter whose site-packages lack polars. CI images, new virtualenvs, and notebooks attached to the wrong kernel are the usual suspects.

## Edge cases
Using `python -m pip` instead of bare pip guarantees the package lands in the interpreter you checked. On very old CPUs, plain polars may then hit the illegal-instruction issue; polars-lts-cpu covers that case.