Switch from black to ruff format (#1515)

* Switch from black to ruff format

Replace black formatter with ruff format across pyproject.toml, Makefile,
CI workflows, and CLAUDE.md. Reformat entire codebase with ruff (line-length=88).
No lint rules added — ruff is used for formatting only.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Exclude malformed notebook from ruff format check

The care-to-learn.ipynb has an invalid notebook schema that causes
ruff to exit with code 2, failing CI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: MaxGhenis

.github/bump_version.py

@@ -19,9 +19,7 @@ def get_current_version(pyproject_path: Path) -> str:
 
 def infer_bump(changelog_dir: Path) -> str:
     fragments = [
-        f
-        for f in changelog_dir.iterdir()
-        if f.is_file() and f.name != ".gitkeep"
+        f for f in changelog_dir.iterdir() if f.is_file() and f.name != ".gitkeep"
     ]
     if not fragments:
         print("No changelog fragments found", file=sys.stderr)

.github/workflows/code_changes.yaml

@@ -17,10 +17,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
         - uses: actions/checkout@v4
+        - name: Install uv
+          uses: astral-sh/setup-uv@v5
         - name: Check formatting
-          uses: "lgeiger/black-action@master"
-          with:
-              args: ". -l 79 --check"
+          run: uvx ruff format --check .
   Test:
       runs-on: macos-latest
       permissions:

.github/workflows/pr_code_changes.yaml

@@ -19,10 +19,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
         - uses: actions/checkout@v4
+        - name: Install uv
+          uses: astral-sh/setup-uv@v5
         - name: Check formatting
-          uses: "lgeiger/black-action@master"
-          with:
-              args: ". -l 79 --check"
+          run: uvx ruff format --check .
   Test:
       runs-on: macos-latest
       permissions:

CLAUDE.md

@@ -6,14 +6,14 @@
 
 ## Build commands
 - Install: `make install` or `pip install -e ".[dev]" --config-settings editable_mode=compat`
-- Format code: `make format` or `black . -l 79`
+- Format code: `make format` or `ruff format .`
 - Run all tests: `make test`
 - Run single test: `pytest policyengine_uk/tests/path/to/test_file.py::test_function -v`
 - Generate documentation: `make documentation`
 - Update changelog: `make changelog`
 
 ## Code Standards
-- **Formatting**: Use Black with 79-character line length
+- **Formatting**: Use Ruff formatter with 88-character line length
 - **Imports**: Group imports by stdlib, third-party, local with each group alphabetized
 - **Naming**: Use snake_case for variables/functions, CamelCase for classes
 - **Type Hints**: Use Python type hints where possible

Makefile

@@ -11,7 +11,7 @@ install:
 	pip install huggingface_hub
 
 format:
-	black . -l 79
+	ruff format .
 
 test:
 	policyengine-core test policyengine_uk/tests/policy -c policyengine_uk

changelog.d/switch-to-ruff.changed.md

@@ -0,0 +1 @@
+Switch from black to ruff format.

docs/book/programs/gov/dcms/bbc/tv-licence.ipynb

@@ -128,12 +128,10 @@
     "\n",
     "df = pd.DataFrame()\n",
     "df[\"Date\"] = [\n",
-    "    parameter.instant_str\n",
-    "    for parameter in dcms.bbc.tv_licence.colour.values_list\n",
+    "    parameter.instant_str for parameter in dcms.bbc.tv_licence.colour.values_list\n",
     "]\n",
     "df[\"Full TV Licence Fee\"] = [\n",
-    "    f\"£{parameter.value:.2f}\"\n",
-    "    for parameter in dcms.bbc.tv_licence.colour.values_list\n",
+    "    f\"£{parameter.value:.2f}\" for parameter in dcms.bbc.tv_licence.colour.values_list\n",
     "]\n",
     "df[\"Blind TV Licence Fee\"] = [\n",
     "    f\"£{0.5 * parameter.value:.2f}\"\n",
@@ -334,9 +332,7 @@
     "    aged_discount[\"Change against current\"] += [\n",
     "        f\"{aged_discount['Reformed value'][i] - 1:.0%}\"\n",
     "    ]\n",
-    "    aged_discount[\"Reformed value\"][\n",
-    "        i\n",
-    "    ] = f\"{aged_discount['Reformed value'][i]:.0%}\"\n",
+    "    aged_discount[\"Reformed value\"][i] = f\"{aged_discount['Reformed value'][i]:.0%}\"\n",
     "    aged_discount[\"Reference\"] += [\n",
     "        f'<a href=\"{reference_list_ad[i]}\">Budgetary impact of changing aged discount to {aged_discount[\"Reformed value\"][i]}</a>'\n",
     "    ]\n",

docs/book/programs/gov/dwp/pension-credit.ipynb

@@ -167,12 +167,8 @@
     "\n",
     "parameters = system.parameters\n",
     "\n",
-    "carer_addition = (\n",
-    "    parameters.gov.dwp.pension_credit.guarantee_credit.carer.addition\n",
-    ")\n",
-    "child_addition = (\n",
-    "    parameters.gov.dwp.pension_credit.guarantee_credit.child.addition\n",
-    ")\n",
+    "carer_addition = parameters.gov.dwp.pension_credit.guarantee_credit.carer.addition\n",
+    "child_addition = parameters.gov.dwp.pension_credit.guarantee_credit.child.addition\n",
     "disabled_child = (\n",
     "    parameters.gov.dwp.pension_credit.guarantee_credit.child.disability.addition\n",
     ")\n",
@@ -1506,12 +1502,8 @@
     "\n",
     "parameters = system.parameters\n",
     "\n",
-    "threshold_single = (\n",
-    "    parameters.gov.dwp.pension_credit.savings_credit.threshold.SINGLE\n",
-    ")\n",
-    "threshold_couple = (\n",
-    "    parameters.gov.dwp.pension_credit.savings_credit.threshold.COUPLE\n",
-    ")\n",
+    "threshold_single = parameters.gov.dwp.pension_credit.savings_credit.threshold.SINGLE\n",
+    "threshold_couple = parameters.gov.dwp.pension_credit.savings_credit.threshold.COUPLE\n",
     "\n",
     "elements = [threshold_single, threshold_couple]  # [...]\n",
     "\n",

docs/book/programs/gov/dwp/universal-credit.ipynb

@@ -194,9 +194,7 @@
     "disabled_child_amount = (\n",
     "    parameters.gov.dwp.universal_credit.elements.child.disabled.amount\n",
     ")\n",
-    "higher_amount = (\n",
-    "    parameters.gov.dwp.universal_credit.elements.child.first.higher_amount\n",
-    ")\n",
+    "higher_amount = parameters.gov.dwp.universal_credit.elements.child.first.higher_amount\n",
     "\n",
     "elements = [\n",
     "    carer_amount,\n",

docs/book/programs/gov/hmrc/child-benefit.ipynb

@@ -175,9 +175,7 @@
     "        data[\"Reference\"] += [\"\"]\n",
     "\n",
     "\n",
-    "for (\n",
-    "    parameter\n",
-    ") in parameters.gov.hmrc.child_benefit.amount.additional.values_list:\n",
+    "for parameter in parameters.gov.hmrc.child_benefit.amount.additional.values_list:\n",
     "    data[\"Date\"] += [parameter.instant_str]\n",
     "    data[\"Name\"] += [\"Additional\"]\n",
     "    data[\"Value\"] += [f\"£{parameter.value:.2f}\"]\n",
@@ -189,9 +187,9 @@
     "        data[\"Reference\"] += [\"\"]\n",
     "\n",
     "\n",
-    "pd.DataFrame(data).sort_values(\"Date\").set_index(\n",
-    "    [\"Date\", \"Name\"]\n",
-    ").style.format(lambda x: x)"
+    "pd.DataFrame(data).sort_values(\"Date\").set_index([\"Date\", \"Name\"]).style.format(\n",
+    "    lambda x: x\n",
+    ")"
    ]
   },
   {
@@ -302,9 +300,7 @@
     "pd.DataFrame(\n",
     "    {\n",
     "        \"Number of children\": list(range(1, 7)),\n",
-    "        \"Child Benefit (Annual)\": list(\n",
-    "            map(get_cb_for_n_children, range(1, 7))\n",
-    "        ),\n",
+    "        \"Child Benefit (Annual)\": list(map(get_cb_for_n_children, range(1, 7))),\n",
     "    }\n",
     ").set_index(\"Number of children\")"
    ]