Support Python 3.9 and 3.10

.github/workflows/pr_code_changes.yaml

@@ -15,6 +15,25 @@ on:
   workflow_dispatch:
 
 jobs:
+  Python-Compat:
+    name: Install + smoke-import (py${{ matrix.python-version }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13", "3.14"]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install uv
+        uses: astral-sh/setup-uv@v5
+      - name: Install package
+        run: uv pip install --system .
+      - name: Smoke-import
+        run: python -c "import policyengine_uk; print('import OK')"
   Lint:
     runs-on: ubuntu-latest
     steps:

changelog.d/support-py39.added.md

@@ -0,0 +1 @@
+Support Python 3.9 and 3.10 (in addition to 3.11–3.14). On Python 3.9/3.10, pip resolves `policyengine-core` to a version that has been relaxed to support older Python (3.24.0+); on 3.11+ behavior is unchanged.

policyengine_uk/data/dataset_schema.py

@@ -1,6 +1,6 @@
 import pandas as pd
 import numpy as np
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, List, Optional
 
 if TYPE_CHECKING:
     from policyengine_uk import Microsimulation
@@ -179,7 +179,7 @@ class UKMultiYearDataset:
     def __init__(
         self,
         file_path: str = None,
-        datasets: list[UKSingleYearDataset] | None = None,
+        datasets: Optional[List[UKSingleYearDataset]] = None,
     ):
         if datasets is not None:
             self.datasets = {}

policyengine_uk/simulation.py

@@ -105,7 +105,7 @@ def __init__(
             Union[pd.DataFrame, str, UKSingleYearDataset, UKMultiYearDataset]
         ] = None,
         trace: bool = False,
-        reform: Dict | Type[Reform] = None,
+        reform: Union[Dict, Type[Reform]] = None,
     ):
         """Initialize a UK simulation.
 

policyengine_uk/tests/test_build_metadata.py

@@ -1,3 +1,4 @@
+from contextlib import ExitStack
 from unittest.mock import patch
 
 from policyengine_uk.build_metadata import (
@@ -19,20 +20,25 @@ def test_data_build_fingerprint_is_stable_within_process():
 def test_get_data_build_metadata_includes_version_git_sha_and_fingerprint():
     get_data_build_fingerprint.cache_clear()
 
-    with (
-        patch(
-            "policyengine_uk.build_metadata._get_package_version",
-            return_value="2.74.0",
-        ),
-        patch(
-            "policyengine_uk.build_metadata._get_git_sha",
-            return_value="deadbeef",
-        ),
-        patch(
-            "policyengine_uk.build_metadata.get_data_build_fingerprint",
-            return_value="sha256:fingerprint",
-        ),
-    ):
+    with ExitStack() as stack:
+        stack.enter_context(
+            patch(
+                "policyengine_uk.build_metadata._get_package_version",
+                return_value="2.74.0",
+            )
+        )
+        stack.enter_context(
+            patch(
+                "policyengine_uk.build_metadata._get_git_sha",
+                return_value="deadbeef",
+            )
+        )
+        stack.enter_context(
+            patch(
+                "policyengine_uk.build_metadata.get_data_build_fingerprint",
+                return_value="sha256:fingerprint",
+            )
+        )
         metadata = get_data_build_metadata()
 
     assert metadata == {

pyproject.toml

@@ -16,18 +16,22 @@ classifiers = [
     "License :: OSI Approved :: GNU Affero General Public License v3",
     "Operating System :: POSIX",
     "Programming Language :: Python",
+    "Programming Language :: Python :: 3.9",
+    "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: 3.14",
     "Topic :: Scientific/Engineering :: Information Analysis",
 ]
-requires-python = ">=3.11"
+requires-python = ">=3.9"
 dependencies = [
     "policyengine-core>=3.23.6",
     "microdf-python>=1.2.1",
     "pydantic>=2.11.7",
-    "tables>=3.10.2",
+    "tables>=3.9.2,<3.10.2; python_version < '3.10'",
+    "tables>=3.10.0,<3.10.2; python_version == '3.10.*'",
+    "tables>=3.10.2; python_version >= '3.11'",
 ]
 
 [project.urls]
@@ -51,6 +55,16 @@ include = [
 [tool.hatch.build.targets.wheel]
 packages = ["policyengine_uk"]
 
+[tool.uv]
+# Until policyengine-core ships 3.9/3.10 support (3.24.0+), restrict
+# uv.lock resolution to >=3.11. `requires-python` above still declares
+# 3.9 is supported — pip users on 3.9/3.10 will resolve against PyPI
+# once core 3.24+ is published. Remove this block once the lockfile
+# can cleanly resolve across 3.9-3.14.
+environments = [
+    "python_version >= '3.11'",
+]
+
 [project.optional-dependencies]
 dev = [
     "ruff>=0.9.0",
@@ -109,6 +123,7 @@ showcontent = true
 
 [tool.ruff]
 line-length = 88
+target-version = "py39"
 extend-exclude = [
     "docs/book/programs/gov/dfe/care-to-learn.ipynb",
 ]