fix(google-cloud-core): Drop support for Python 3.9 (googleapis#16953)

This PR updates \`google-cloud-core\` to establish Python 3.10 as the
minimum supported version, dropping support for Python 3.7, 3.8, and
3.9.

### Changes

* Configuration: Updated \`setup.py\` and \`noxfile.py\` to require
Python 3.10+ and remove references to Python 3.9.
* Documentation: Updated \`README.rst\` and \`CONTRIBUTING.rst\` to
reflect supported Python versions.
* Cleanup: Removed dead polyfill for \`importlib.metadata\` in
\`google/cloud/obsolete/__init__.py\`.
* Constraints: Transferred lower bounds to \`constraints-3.10.txt\` and
dropped \`constraints-3.9.txt\`.
* Fixes: Bumped \`grpcio\` to \`1.47.0\` to fix Python 3.10 build
failures.

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

Author: chalmerlowe

packages/google-cloud-core/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
@@ -197,14 +197,12 @@ 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/
@@ -217,17 +215,6 @@ Supported versions can be found in our ``noxfile.py`` `config`_.
 .. _config: https://github.com/googleapis/google-cloud-python/blob/main/noxfile.py
 
 
-We also explicitly decided to support Python 3 beginning with version 3.9.
-Reasons for this include:
-
--  Encouraging use of newest versions of Python 3
--  Taking the lead of `prominent`_ open-source `projects`_
--  `Unicode literal support`_ which allows for a cleaner codebase that
-   works in both Python 2 and Python 3
-
-.. _prominent: https://docs.djangoproject.com/en/1.9/faq/install/#what-python-version-can-i-use-with-django
-.. _projects: http://flask.pocoo.org/docs/0.10/python3/
-.. _Unicode literal support: https://www.python.org/dev/peps/pep-0414/
 
 **********
 Versioning

packages/google-cloud-core/README.rst

@@ -32,9 +32,8 @@ to `Python Development Environment Setup Guide`_ for Google Cloud Platform.
 
 Supported Python Versions
 -------------------------
-Python >= 3.9
+Python >= 3.10
 
 Unsupported Python Versions
 ---------------------------
-
-Python <= 3.8
+Python <= 3.9

packages/google-cloud-core/docs/README.rst

@@ -32,9 +32,8 @@ to `Python Development Environment Setup Guide`_ for Google Cloud Platform.
 
 Supported Python Versions
 -------------------------
-Python >= 3.9
+Python >= 3.10
 
 Unsupported Python Versions
 ---------------------------
-
-Python <= 3.8
+Python <= 3.9

packages/google-cloud-core/google/cloud/obsolete/__init__.py

@@ -14,11 +14,7 @@
 
 """Helpers for deprecated code and modules."""
 
-try:
-    import importlib.metadata as metadata
-except ImportError:
-    # For Python 3.7 compatibility
-    import importlib_metadata as metadata  # type: ignore[no-redef]
+import importlib.metadata as metadata
 
 import warnings
 

packages/google-cloud-core/noxfile.py

@@ -26,7 +26,6 @@
 
 DEFAULT_PYTHON_VERSION = "3.14"
 UNIT_TEST_PYTHON_VERSIONS = [
-    "3.9",
     "3.10",
     "3.11",
     "3.12",

packages/google-cloud-core/pytest.ini

@@ -4,11 +4,9 @@ filterwarnings =
     error
     # Remove once https://github.com/protocolbuffers/protobuf/issues/12186 is fixed
     ignore:.*custom tp_new.*in Python 3.14:DeprecationWarning
-    # Remove after support for Python 3.7 is dropped
-    ignore:After January 1, 2024, new releases of this library will drop support for Python 3.7:DeprecationWarning
     # Remove once the minimum supported version of `google-api-core` is 2.15.0
     ignore:.*pkg_resources.declare_namespace:DeprecationWarning
     ignore:.*pkg_resources is deprecated as an API:DeprecationWarning
-    # Remove after support for Python 3.8, 3.9 and/or 3.10+ is dropped
+    # Remove after support for Python 3.10+ is dropped
     ignore:\s*You are using a (non-supported )?Python version \(?3\.(8|9|1[0-9]+):DeprecationWarning
     ignore:\s*You are using a (non-supported )?Python version \(?3\.(8|9|1[0-9]+):FutureWarning

packages/google-cloud-core/setup.py

@@ -33,9 +33,9 @@
 ]
 extras = {
     "grpc": [
-        "grpcio >= 1.38.0, < 2.0.0; python_version < '3.14'",
+        "grpcio >= 1.47.0, < 2.0.0; python_version < '3.14'",
         "grpcio >= 1.75.1, < 2.0.0; python_version >= '3.14'",
-        "grpcio-status >= 1.38.0, < 2.0.0",
+        "grpcio-status >= 1.47.0, < 2.0.0",
     ],
 }
 
@@ -75,7 +75,6 @@
         "License :: OSI Approved :: Apache Software License",
         "Programming Language :: Python",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: 3.10",
         "Programming Language :: Python :: 3.11",
         "Programming Language :: Python :: 3.12",
@@ -88,7 +87,7 @@
     packages=packages,
     install_requires=dependencies,
     extras_require=extras,
-    python_requires=">=3.9",
+    python_requires=">=3.10",
     include_package_data=True,
     zip_safe=False,
 )

packages/google-cloud-core/testing/constraints-3.10.txt

@@ -0,0 +1,13 @@
+# This constraints file is used to check that lower bounds
+# are correct in setup.py
+# List *all* library dependencies and extras in this file.
+# Pin the version to the lower bound.
+#
+# e.g., if setup.py has "foo >= 1.14.0, < 2.0.0dev",
+# Then this file should have foo==1.14.0
+google-api-core==2.11.0
+google-auth==2.14.1
+grpcio==1.47.0
+grpcio-status==1.47.0
+# cryptography is a direct dependency of google-auth
+cryptography==38.0.3