ModuleNotFoundError: No module named 'fastparquet'

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

ModuleNotFoundError: No module named 'fastparquet'

Fix it

1. Install an engine:

   pip install fastparquet

   Expected: install completes.

2. Verify:

   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 readparquet or toparquet 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.

GitHub issue pandas-dev/pandas#18156 reports ModuleNotFoundError: No module named 'fastparquet' when using pandas parquet IO without an engine installed. The verified fix: installing an engine, either pip install fastparquet or pip install pyarrow, after which read_parquet works. Full thread: https://github.com/pandas-dev/pandas/issues/18156