feat: Add Python 3.14 support (#327)

This PR adds support for Python 3.14 to the library.

Key changes include:

* Adding Python 3.14 to the test matrix in
`.github/workflows/unittest.yml`, etc.
* Updating `setup.py` to include the Python 3.14 classifier
* Adding `testing/constraints-3.14.txt`.
* Updating `noxfile.py` to include 3.14 sessions.
* Updates `CONTRIBUTING.rst` to list Python 3.14 as a supported version.

Towards internal issue: b/375664027

Author: chalmerlowe

.github/workflows/lint.yml

@@ -12,7 +12,7 @@ jobs:
     - name: Setup Python
       uses: actions/setup-python@v5
       with:
-        python-version: "3.8"
+        python-version: "3.14"
     - name: Install nox
       run: |
         python -m pip install --upgrade setuptools pip wheel

.github/workflows/unittest.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-22.04
     strategy:
       matrix:
-        python: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12', '3.13']
+        python: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12', '3.13', '3.14']
     steps:
     - name: Checkout
       uses: actions/checkout@v4
@@ -45,7 +45,7 @@ jobs:
     - name: Setup Python
       uses: actions/setup-python@v5
       with:
-        python-version: "3.8"
+        python-version: "3.14"
     - name: Install coverage
       run: |
         python -m pip install --upgrade setuptools pip wheel

CONTRIBUTING.rst

@@ -22,7 +22,7 @@ In order to add a feature:
   documentation.
 
 - The feature must work fully on the following CPython versions:
-  3.7, 3.8, 3.9, 3.10, 3.11, 3.12 and 3.13 on both UNIX and Windows.
+  3.7, 3.8, 3.9, 3.10, 3.11, 3.12, 3.13 and 3.14 on both UNIX and Windows.
 
 - The feature must not add unnecessary dependencies (where
   "unnecessary" is of course subjective, but new dependencies should
@@ -228,6 +228,7 @@ We support:
 -  `Python 3.11`_
 -  `Python 3.12`_
 -  `Python 3.13`_
+-  `Python 3.14`_
 
 .. _Python 3.7: https://docs.python.org/3.7/
 .. _Python 3.8: https://docs.python.org/3.8/
@@ -236,6 +237,7 @@ We support:
 .. _Python 3.11: https://docs.python.org/3.11/
 .. _Python 3.12: https://docs.python.org/3.12/
 .. _Python 3.13: https://docs.python.org/3.13/
+.. _Python 3.14: https://docs.python.org/3.14/
 
 
 Supported versions can be found in our ``noxfile.py`` `config`_.

noxfile.py

@@ -32,7 +32,7 @@
 ISORT_VERSION = "isort==5.11.0"
 LINT_PATHS = ["docs", "google", "tests", "noxfile.py", "setup.py"]
 
-DEFAULT_PYTHON_VERSION = "3.8"
+DEFAULT_PYTHON_VERSION = "3.14"
 
 UNIT_TEST_PYTHON_VERSIONS: List[str] = [
     "3.7",
@@ -42,6 +42,7 @@
     "3.11",
     "3.12",
     "3.13",
+    "3.14",
 ]
 UNIT_TEST_STANDARD_DEPENDENCIES = [
     "mock",
@@ -56,7 +57,7 @@
 UNIT_TEST_EXTRAS: List[str] = []
 UNIT_TEST_EXTRAS_BY_PYTHON: Dict[str, List[str]] = {}
 
-SYSTEM_TEST_PYTHON_VERSIONS: List[str] = ["3.8"]
+SYSTEM_TEST_PYTHON_VERSIONS: List[str] = ["3.12"]
 SYSTEM_TEST_STANDARD_DEPENDENCIES: List[str] = [
     "mock",
     "pytest",
@@ -135,7 +136,7 @@ def format(session):
 @nox.session(python=DEFAULT_PYTHON_VERSION)
 def lint_setup_py(session):
     """Verify that setup.py is valid (including RST check)."""
-    session.install("docutils", "pygments")
+    session.install("docutils", "pygments", "setuptools")
     session.run("python", "setup.py", "check", "--restructuredtext", "--strict")
 
 
@@ -175,7 +176,12 @@ def install_unittest_dependencies(session, *constraints):
 def unit(session, protobuf_implementation):
     # Install all test dependencies, then install this package in-place.
 
-    if protobuf_implementation == "cpp" and session.python in ("3.11", "3.12", "3.13"):
+    if protobuf_implementation == "cpp" and session.python in (
+        "3.11",
+        "3.12",
+        "3.13",
+        "3.14",
+    ):
         session.skip("cpp implementation is not supported in python 3.11+")
 
     constraints_path = str(
@@ -375,7 +381,7 @@ def docfx(session):
     )
 
 
-@nox.session(python="3.13")
+@nox.session(python="3.14")
 @nox.parametrize(
     "protobuf_implementation",
     ["python", "upb", "cpp"],

setup.py

@@ -81,6 +81,7 @@
         "Programming Language :: Python :: 3.11",
         "Programming Language :: Python :: 3.12",
         "Programming Language :: Python :: 3.13",
+        "Programming Language :: Python :: 3.14",
         "Operating System :: OS Independent",
         "Topic :: Internet",
     ],