Add support for free-threaded Python (PEP 703)

Builds on #940 — completes the remaining work for free-threaded support.

Rust:
- Add `gil_used = false` to `#[pymodule]` (PyO3 0.27 defaults to true)
- Codebase has zero global state, zero unsafe — all functions are pure

CI (tests.yml):
- Add 3.13t and 3.14t to test matrix
- Skip mypy/typing deps for free-threaded builds (not yet compatible)

CI (release.yml):
- Add free-threaded wheel build step (3.13t/3.14t) in the build job
- Skipped for PyPy matrix entries

Tests:
- Add concurrent thread-safety tests for parse, now, duration, diff, format

Author: Gaganraj2002

.github/workflows/release.yml

@@ -70,6 +70,16 @@ jobs:
           rust-toolchain: stable
           docker-options: -e CI
 
+      - name: build free-threaded wheels
+        uses: PyO3/maturin-action@86b9d133d34bc1b40018696f782949dac11bd380 # v1.49.4
+        if: ${{ !contains(matrix.interpreter || '', 'pypy') }}
+        with:
+          target: ${{ matrix.target }}
+          manylinux: ${{ matrix.manylinux || 'auto' }}
+          args: --release --out dist --interpreter 3.13t 3.14t
+          rust-toolchain: stable
+          docker-options: -e CI
+
       - run: ${{ matrix.ls || 'ls -lh' }} dist/
 
       - uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0

.github/workflows/tests.yml

@@ -33,7 +33,7 @@ jobs:
     strategy:
       matrix:
         os: [Ubuntu, MacOS, Windows]
-        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14", "3.13t", "3.14t"]
     defaults:
       run:
         shell: bash
@@ -73,16 +73,23 @@ jobs:
 
       - name: Install runtime, testing, and typing dependencies
         run: poetry install --only main --only test --only typing --only build --no-root -vvv
+        if: ${{ !endsWith(matrix.python-version, 't') }}
+
+      - name: Install runtime and testing dependencies (free-threaded)
+        run: poetry install --only main --only test --only build --no-root -vvv
+        if: ${{ endsWith(matrix.python-version, 't') }}
 
       - name: Install project
         run: poetry run maturin develop
 
       - name: Run type checking
         run: poetry run mypy
+        if: ${{ !endsWith(matrix.python-version, 't') }}
 
       - name: Uninstall typing dependencies
         # This ensures pendulum runs without typing_extensions installed
         run: poetry sync --only main --only test --only build --no-root -vvv
+        if: ${{ !endsWith(matrix.python-version, 't') }}
 
       - name: Test Pure Python
         run: |

rust/src/python/mod.rs

@@ -8,7 +8,7 @@ use helpers::{days_in_year, is_leap, is_long_year, local_time, precise_diff, wee
 use parsing::parse_iso8601;
 use types::{Duration, PreciseDiff};
 
-#[pymodule]
+#[pymodule(gil_used = false)]
 pub fn _pendulum(_py: Python<'_>, m: &Bound<PyModule>) -> PyResult<()> {
     m.add_function(wrap_pyfunction!(days_in_year, m)?)?;
     m.add_function(wrap_pyfunction!(is_leap, m)?)?;

tests/test_thread_safety.py

@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+import concurrent.futures
+
+import pendulum
+
+
+ITERATIONS = 200
+WORKERS = 8
+
+
+def _run_parallel(fn, *args):
+    with concurrent.futures.ThreadPoolExecutor(max_workers=WORKERS) as pool:
+        futures = [pool.submit(fn, *args) for _ in range(ITERATIONS)]
+        return [f.result() for f in futures]
+
+
+def test_parse_iso8601_threaded():
+    results = _run_parallel(pendulum.parse, "2024-01-15T10:30:00+00:00")
+    expected = results[0]
+    assert all(r == expected for r in results)
+
+
+def test_now_threaded():
+    results = _run_parallel(pendulum.now)
+    assert all(isinstance(r, pendulum.DateTime) for r in results)
+
+
+def test_duration_threaded():
+    def make_duration():
+        return pendulum.duration(years=1, months=2, days=3)
+
+    results = _run_parallel(make_duration)
+    assert all(r.years == 1 and r.months == 2 for r in results)
+
+
+def test_diff_threaded():
+    dt1 = pendulum.datetime(2024, 1, 1)
+    dt2 = pendulum.datetime(2024, 6, 15)
+
+    def compute_diff():
+        return dt1.diff(dt2)
+
+    results = _run_parallel(compute_diff)
+    expected = results[0]
+    assert all(r.in_days() == expected.in_days() for r in results)
+
+
+def test_format_threaded():
+    dt = pendulum.datetime(2024, 1, 15, 10, 30, 0)
+
+    def format_dt():
+        return dt.format("YYYY-MM-DD HH:mm:ss")
+
+    results = _run_parallel(format_dt)
+    assert all(r == "2024-01-15 10:30:00" for r in results)