papermill-tests

Papermill executes notebooks programmatically with injected parameters, producing an output notebook with results. Per the Papermill execute docs, it pairs naturally with regression testing: run a parameterized notebook in CI, assert on outputs.

When to use

• Parameterized analysis notebooks: same notebook, different inputs (per-region, per-month, per-customer-segment).
• Production-grade notebook execution (Airflow / Argo / Prefect / cron) - papermill is the standard executor.
• Regression test: re-run the notebook with known inputs; assert output values match expected (often paired with nbval/testbook).

How to use

1. pip install papermill (Step 1).
2. Tag one notebook cell parameters with default values (Step 2).
3. Execute with injected inputs via the Python API pm.execute_notebook(...) or the CLI papermill in.ipynb out.ipynb -p NAME VAL (Steps 3-4).
4. Read the output notebook with nbformat and assert on the final cell's values inside a pytest test (Step 5).
5. Always seed stochastic parameters (-p seed N) so reruns are reproducible.
6. Upload the output notebook as a CI artifact so failed assertions stay inspectable (Step 6).
7. Layer nbval / testbook on top of papermill's execution for output and function-level assertions (Step 7).

Step 1 - Install

pip install papermill

Per the Papermill execute docs.

Step 2 - Tag the parameters cell

In your notebook, tag one cell with parameters:

# Cell tagged "parameters"
alpha = 0.5
ratio = 0.2
input_path = "data/sales.parquet"

Papermill replaces these with injected values at execution time (adds an injected-parameters cell after the tagged cell).

Step 3 - Python API execution

import papermill as pm

pm.execute_notebook(
    'path/to/input.ipynb',
    'path/to/output.ipynb',
    parameters=dict(alpha=0.6, ratio=0.1)
)

Per the Papermill execute docs.

Step 4 - CLI execution

# Local in/out
papermill local/input.ipynb local/output.ipynb -p alpha 0.6 -p ratio 0.1

# S3 output
papermill local/input.ipynb s3://bkt/output.ipynb -p alpha 0.6 -p l1_ratio 0.1

Parameter flags per the Papermill execute docs:

Step 5 - Use as regression test

import json
import papermill as pm
import nbformat

def test_analysis_with_known_inputs(tmp_path):
    out_path = tmp_path / "out.ipynb"
    pm.execute_notebook(
        'analysis.ipynb',
        str(out_path),
        parameters=dict(seed=42, n_samples=1000),
    )

    nb = nbformat.read(str(out_path), as_version=4)
    final_cell = nb.cells[-1]
    output_text = final_cell.outputs[0]['text']
    result = json.loads(output_text)

    assert abs(result['mean'] - 0.5) < 0.01
    assert result['n'] == 1000

The output notebook is artifact-friendly - attach to CI runs for review when assertions fail.

Step 6 - Parameter sweeps in CI

# GitHub Actions matrix sweep
strategy:
  matrix:
    seed: [42, 123, 7]
    n_samples: [100, 1000]
steps:
  - run: |
      papermill analysis.ipynb out-${{ matrix.seed }}-${{ matrix.n_samples }}.ipynb \
        -p seed ${{ matrix.seed }} \
        -p n_samples ${{ matrix.n_samples }}
  - uses: actions/upload-artifact@v4
    with:
      name: papermill-output-${{ matrix.seed }}-${{ matrix.n_samples }}
      path: out-${{ matrix.seed }}-${{ matrix.n_samples }}.ipynb

Step 7 - Pair with nbval / testbook

Papermill is the engine; nbval and testbook are the assertion layers. Use all three for production notebook QA.

Step 8 - TQDM progress descriptions

Add comments at cell start:

#papermill_description=load_data
df = load_dataset()

#papermill_description=train_model
model.fit(df)

Per the Papermill execute docs: integrates with TQDM for meaningful CI progress indicators.

Worked example

An analyst ships analysis.ipynb that samples a distribution and prints a JSON summary in its last cell. To gate it in CI:

1. Tag the top cell parameters with defaults seed = 0 and n_samples = 100.
2. Add a pytest test that runs pm.execute_notebook('analysis.ipynb', out_path, parameters=dict(seed=42, n_samples=1000)).
3. Read out.ipynb with nbformat, parse the last cell's output text as JSON, and assert abs(result['mean'] - 0.5) < 0.01 and result['n'] == 1000.

On a green run the assertions pass and out.ipynb uploads as a CI artifact. When a refactor shifts the sampled mean, the assertion fails, the job goes red, and the attached output notebook shows the offending cell for review.

Anti-patterns

Limitations

• Papermill executes via the standard Jupyter kernel; very long notebooks have higher OOM risk than equivalent .py scripts.
• Output notebooks are large (full re-render of all cells); CI artifact storage adds up - consider retention policy.
• Parameter injection is one-shot at notebook start; cannot re-parameterize mid-run.

References

• Papermill execute docs - Python API, CLI, parameter flags, TQDM integration