TL;DR: fastparquet's compiled speed-up module did not build during install. Reinstall fastparquet with a working C compiler (or grab a prebuilt wheel) and the import works.

## The error
```text
ModuleNotFoundError: No module named 'fastparquet.cencoding'
```

## Fix it
1. Reinstall fastparquet, letting pip pick a prebuilt wheel:
   ```
   pip install --force-reinstall fastparquet
   ```
   Expected: installs a wheel that already contains cencoding.
2. If pip builds from source instead, install a C compiler first (Debian/Ubuntu: `sudo apt install build-essential`; then rerun the reinstall). Expected: the build compiles cencoding.
3. Verify:
   ```
   python -c "import fastparquet; print(fastparquet.__version__)"
   ```
   Expected: prints the version, no error.

## When this applies
Use this when `import fastparquet` raises the cencoding error, typical on platforms without a matching wheel.

## When it does not apply
If the error is plain No module named 'fastparquet', just install it. If cencoding imports but reads are wrong, that is a data issue, not this one.

## Compatibility
fastparquet installs that compile the optional C extension; wheels for major platforms already include it.

## Root cause
fastparquet ships an optional Cython extension (cencoding) for speed. Source installs without a compiler silently skip it, and the import of the extension module then fails.

## Edge cases
fastparquet works in pure-python mode without cencoding, just slower; the import error only bites because the package tries the extension first. Pinning fastparquet in CI avoids surprise source builds.