TL;DR: pandas needs a parquet engine and fastparquet is the one your code asked for. Run `pip install fastparquet` (pyarrow works too) and the read succeeds.

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

## Fix it
1. Install an engine:
   ```
   pip install fastparquet
   ```
   Expected: install completes.
2. Verify:
   ```python
   import pandas as pd
   df = pd.read_parquet("data.parquet", engine="fastparquet")
   print(df.head())
   ```
   Expected: prints the first rows.
3. Alternative engine: `pip install pyarrow` and omit the engine argument.

## When this applies
Use this when read_parquet or to_parquet raises the fastparquet error.

## When it does not apply
If the error is the missing-pyarrow message, install pyarrow instead. If an engine is installed but the file will not read, the file may be corrupt.

## Compatibility
All pandas versions with parquet support.

## Root cause
pandas delegates parquet to an external engine and ships with none selected by default. Code (or pandas' own engine preference) asking for fastparquet fails when it was never installed.

## Edge cases
pyarrow is the recommended engine for new code; fastparquet stays useful for older files. In notebooks, restart the kernel after installing so the new package is visible.