chore: remove references to Python 3.8 and 3.9 (#16940)

This PR updates `pandas-gbq` to establish Python 3.10 as the minimum
supported version, dropping support for Python 3.9 and below.

### Changes

* Configuration: Updated `noxfile.py` to remove references to Python 3.9
and remove dead skip logic for 3.9.
* Documentation: Updated `CONTRIBUTING.rst` to reflect the new supported
Python versions and update Nox examples.
* Runtime Check: Updated the runtime version check in
`pandas_gbq/__init__.py` to warn for versions older than 3.10.

Fixes internal issue: http://b/482126936 🦕

Author: chalmerlowe

packages/pandas-gbq/CONTRIBUTING.rst

@@ -22,7 +22,7 @@ In order to add a feature:
   documentation.
 
 - The feature must work fully on the following CPython versions:
-  3.9, 3.10, 3.11, 3.12, 3.13 and 3.14 on both UNIX and Windows.
+  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
@@ -195,11 +195,11 @@ configure them just like the System Tests.
 
    # Run all tests in a folder
    $ cd samples/snippets
-   $ nox -s py-3.8
+   $ nox -s py-3.10
 
    # Run a single sample test
    $ cd samples/snippets
-   $ nox -s py-3.8 -- -k <name of test>
+   $ nox -s py-3.10 -- -k <name of test>
 
 ********************************************
 Note About ``README`` as it pertains to PyPI
@@ -221,14 +221,12 @@ Supported Python Versions
 
 We support:
 
--  `Python 3.9`_
 -  `Python 3.10`_
 -  `Python 3.11`_
 -  `Python 3.12`_
 -  `Python 3.13`_
 -  `Python 3.14`_
 
-.. _Python 3.9: https://docs.python.org/3.9/
 .. _Python 3.10: https://docs.python.org/3.10/
 .. _Python 3.11: https://docs.python.org/3.11/
 .. _Python 3.12: https://docs.python.org/3.12/
@@ -241,7 +239,7 @@ Supported versions can be found in our ``noxfile.py`` `config`_.
 .. _config: https://github.com/googleapis/google-cloud-python/blob/main/packages/pandas-gbq/noxfile.py
 
 
-We also explicitly decided to support Python 3 beginning with version 3.9.
+We also explicitly decided to support Python 3 beginning with version 3.10.
 Reasons for this include:
 
 -  Encouraging use of newest versions of Python 3

packages/pandas-gbq/noxfile.py

@@ -40,10 +40,6 @@
     "3.12",
     "3.13",
     "3.14",
-    # Not supported, but included so that we can explicitly skip the session
-    # from here. Keep unsupported versions last so that they don't conflict with
-    # the prerelease_deps session.
-    "3.9",
 ]
 
 UNIT_TEST_STANDARD_DEPENDENCIES = [
@@ -235,8 +231,6 @@ def default(session):
 @_calculate_duration
 def unit(session):
     """Run the unit test suite."""
-    if session.python == "3.9":
-        session.skip("Python 3.9 is not supported.")
     default(session)
 
 

packages/pandas-gbq/pandas_gbq/__init__.py

@@ -3,22 +3,20 @@
 # license that can be found in the LICENSE file.
 
 import logging
+import sys
 import warnings
 
 from pandas_gbq import version as pandas_gbq_version
 from pandas_gbq.contexts import Context, context
 from pandas_gbq.core.sample import sample
 
-from . import _versions_helpers
 from .gbq import read_gbq, to_gbq  # noqa
 
-sys_major, sys_minor, sys_micro = _versions_helpers.extract_runtime_version()
-if sys_major == 3 and sys_minor < 9:
+if sys.version_info < (3, 10):
     warnings.warn(
-        "pandas-gbq no longer supports Python versions older than 3.9. "
-        "Your Python version is "
-        f"{sys_major}.{sys_minor}.{sys_micro}. Please update "
-        "to Python 3.9 or newer to ensure ongoing support. For more details, "
+        "pandas-gbq no longer supports Python versions older than 3.10. "
+        f"Your Python version is {sys.version_info.major}.{sys.version_info.minor}.{sys.version_info.micro}. "
+        "Please update to Python 3.10 or newer to ensure ongoing support. For more details, "
         "see: https://cloud.google.com/python/docs/supported-python-versions",
         FutureWarning,
     )