Apply stricter ruff linting rules to documentation notebooks

[drbenvincent]

Background

We recently added stricter ruff linting rules (#571) to the codebase (B, F, UP, C4, SIM) to catch potential bugs and enforce modern Python patterns. However, documentation notebooks in docs/ are currently excluded from these checks.

Current State

The .pre-commit-config.yaml file has this exclusion:

- id: ruff
  types_or: [ python, pyi, jupyter ]
  args: [ --fix ]
  # Exclude docs/ to avoid applying strict linting rules to example notebooks
  # Remove this exclusion if you want to enforce strict rules on documentation
  exclude: ^docs/

Issues Found in Notebooks

When running ruff check docs/ the following issues are detected:

• B006: Mutable default arguments (e.g., priors={}) - can cause subtle bugs
• B905: Missing strict= parameter in zip() calls - prevents length mismatches
• B018: Useless expressions (e.g., df_long on its own line)
• Other minor style improvements

NOTE:

We will want to suppress B018 when applied to notebooks. Can do with this change to pyproject.toml:

[tool.ruff.lint.per-file-ignores]
# Allow useless expressions in notebooks (used to display dataframes/outputs)
"*.ipynb" = ["B018"]

Proposed Action

Fix the linting issues in documentation notebooks to:

1. Ensure example code follows best practices
2. Avoid teaching patterns that could lead to bugs
3. Maintain consistency between source code and documentation

Implementation

Run the following to auto-fix most issues:

ruff check --fix --unsafe-fixes docs/

Then manually review and fix any remaining issues. Once complete, remove the exclude: ^docs/ line from .pre-commit-config.yaml.

Affected Files

Based on the last check, approximately 12 issues across these notebooks:

• docs/source/knowledgebase/structural_causal_models.ipynb
• docs/source/notebooks/did_pymc_banks.ipynb
• docs/source/notebooks/inv_prop_latent.ipynb
• docs/source/notebooks/its_lift_test.ipynb
• docs/source/notebooks/iv_weak_instruments.ipynb

Priority

Low - This is a code quality improvement for documentation. The examples work correctly, but would benefit from following stricter best practices.