chore(nox): make Python 3.12 the minimum and stop linting on 3.10 (#14784)

Problem: the shared nox config and the GitHub lint job still targeted
Python 3.10, which reached end of life in Oct 2026. Most samples only
tested 3.10 and 3.14, and linting used each sample's oldest tested
version. So contributors working on 3.12 were asked for a 3.10
interpreter and saw py-3.12 skipped.

Solution:
- noxfile-template.py: ALL_VERSIONS is now 3.12-3.15 and the default
  tests 3.12 + 3.14. Lint always runs on 3.12. A new
  OPT_IN_VERSIONS / "opt_in_versions" setting keeps 3.15 off unless a
  sample asks for it, because existing configs only list the versions
  they skip.
- noxfile_config.py: the default tests 3.12 + 3.14 and documents how
  to opt in to 3.13 and 3.15.
- .github: the lint job and noxfile-lint.py use 3.12. Also fixes two
  flake8 issues and black formatting that were already in the file.

Old version strings such as "3.8" in per-sample configs are now
ignored. Per-sample configs still need updating to test 3.12; that's
planned for a follow-up PR.

Signed-off-by: Jennifer Davis <sigje@google.com>

Author: iennae

.github/scripts/noxfile-lint.py

@@ -19,7 +19,7 @@
 import nox
 
 # Use a stable Python version for running the style utilities
-LINTING_VERSION = "3.10"
+LINTING_VERSION = "3.12"
 
 # Error out if the runner is missing the target python interpreter
 nox.options.error_on_missing_interpreters = True
@@ -33,11 +33,15 @@ def _determine_local_import_names(start_dir: str) -> list[str]:
             basename
             for basename, extension in file_ext_pairs
             if extension == ".py"
-            or (os.path.isdir(os.path.join(start_dir, basename)) and basename != "__pycache__")
+            or (
+                os.path.isdir(os.path.join(start_dir, basename))
+                and basename != "__pycache__"
+            )
         ]
     except Exception:
         return []
 
+
 # Linting with flake8.
 #
 # We ignore the following rules:
@@ -88,7 +92,7 @@ def lint(session: nox.sessions.Session) -> None:
 def blacken(session: nox.sessions.Session) -> None:
     """Runs black code formatting checks. Honors incremental PR file arguments."""
     session.install("black")
-    
+
     # If explicit target files are passed via posargs, target ONLY those files.
     if session.posargs:
         targets = session.posargs

.github/workflows/lint.yml

@@ -27,7 +27,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@6d4fd22b20465ccc0f7354476588e8df7c9ca0e0 # v7.1.0
         with:
-          python-version: '3.10'
+          python-version: '3.12'
 
       - name: Install nox
         run: |

noxfile-template.py

@@ -23,7 +23,6 @@
 
 import nox
 
-
 # WARNING - WARNING - WARNING - WARNING - WARNING
 # WARNING - WARNING - WARNING - WARNING - WARNING
 #       BE CAREFUL WHEN EDITING THIS FILE!
@@ -40,7 +39,12 @@
 
 TEST_CONFIG = {
     # You can opt out from the test for specific Python versions.
-    "ignored_versions": ["2.7", "3.7", "3.8", "3.10", "3.11", "3.12"],
+    # By default, samples are tested on the minimum (3.12) and the
+    # latest stable (3.14) supported Python versions.
+    "ignored_versions": ["3.13"],
+    # Newly released Python versions are only tested when a sample
+    # explicitly opts in, for example: "opt_in_versions": ["3.15"].
+    "opt_in_versions": [],
     # Old samples are opted out of enforcing Python type hints
     # All new samples should feature them
     "enforce_type_hints": False,
@@ -87,20 +91,33 @@ def get_pytest_env_vars() -> dict[str, str]:
     return ret
 
 
-# All versions used to tested samples.
-ALL_VERSIONS = ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13", "3.14"]
+# All Python versions that samples can be tested on. 3.12 is the minimum
+# supported version.
+ALL_VERSIONS = ["3.12", "3.13", "3.14", "3.15"]
+
+# Newly released versions that are only tested when a sample lists them
+# in "opt_in_versions". Existing configs only list the versions they
+# ignore, so without this a new version would be enabled for all of them.
+OPT_IN_VERSIONS = ["3.15"]
 
-# Any default versions that should be ignored.
+# Any default versions that should be ignored. Versions that are no
+# longer in ALL_VERSIONS (for example "3.8") are safely ignored.
 IGNORED_VERSIONS = TEST_CONFIG["ignored_versions"]
 
-TESTED_VERSIONS = sorted([v for v in ALL_VERSIONS if v not in IGNORED_VERSIONS])
+TESTED_VERSIONS = sorted(
+    [
+        v
+        for v in ALL_VERSIONS
+        if v not in IGNORED_VERSIONS
+        and (v not in OPT_IN_VERSIONS or v in TEST_CONFIG.get("opt_in_versions", []))
+    ]
+)
 
 INSTALL_LIBRARY_FROM_SOURCE = bool(os.environ.get("INSTALL_LIBRARY_FROM_SOURCE", False))
 
-# Use the oldest tested Python version for linting (defaults to 3.10)
-LINTING_VERSION = "3.10"
-if len(TESTED_VERSIONS) > 0:
-    LINTING_VERSION = TESTED_VERSIONS[0]
+# Run style checks on the minimum supported Python version, regardless of
+# which versions a sample is tested on, so contributors only need 3.12.
+LINTING_VERSION = "3.12"
 
 # Error if a python version is missing
 nox.options.error_on_missing_interpreters = True

noxfile_config.py

@@ -22,7 +22,13 @@
 
 TEST_CONFIG_OVERRIDE = {
     # You can opt out from the test for specific Python versions.
-    "ignored_versions": ["3.8", "3.9", "3.11", "3.12", "3.13"],
+    # By default, samples are tested on the minimum (3.12) and the
+    # latest stable (3.14) supported Python versions. Remove "3.13"
+    # from this list to also test on 3.13.
+    "ignored_versions": ["3.13"],
+    # Newly released Python versions are only tested when listed here,
+    # for example: "opt_in_versions": ["3.15"].
+    "opt_in_versions": [],
     # Old samples are opted out of enforcing Python type hints
     # All new samples should feature them
     "enforce_type_hints": True,