fix(bigframes): Drop support for Python <= 3.9

packages/bigframes/CONTRIBUTING.rst

@@ -232,11 +232,11 @@ 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
@@ -276,17 +276,7 @@ Supported versions can be found in our ``noxfile.py`` `config`_.
 .. _config: https://github.com/googleapis/google-cloud-python/blob/main/packages/bigframes/noxfile.py
 
 
-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
--  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/bigframes/noxfile.py

@@ -60,7 +60,7 @@
 
 DEFAULT_PYTHON_VERSION = "3.14"
 
-ALL_PYTHON = ["3.9", "3.10", "3.11", "3.12", "3.13", "3.14"]
+ALL_PYTHON = ["3.10", "3.11", "3.12", "3.13", "3.14"]
 UNIT_TEST_STANDARD_DEPENDENCIES = [
     "mock",
     PYTEST_VERSION,
@@ -274,8 +274,6 @@ def run_unit(session, install_test_extra):
 @nox.session(python=ALL_PYTHON)
 @nox.parametrize("test_extra", [True, False])
 def unit(session, test_extra):
-    if session.python in ("3.7", "3.8", "3.9"):
-        session.skip("Python 3.9 and below are not supported")
     if test_extra:
         run_unit(session, install_test_extra=test_extra)
     else:
@@ -378,9 +376,6 @@ def run_system(
 @nox.session(python="3.12")
 def system(session: nox.sessions.Session):
     """Run the system test suite."""
-    if session.python in ("3.7", "3.8", "3.9"):
-        session.skip("Python 3.9 and below are not supported")
-
     run_system(
         session=session,
         prefix_name="system",

packages/bigframes/tests/unit/test_pandas.py

@@ -54,11 +54,6 @@ def all_session_methods():
     [(method_name,) for method_name in all_session_methods()],
 )
 def test_method_matches_session(method_name: str):
-    if sys.version_info < (3, 10):
-        pytest.skip(
-            "Need Python 3.10 to reconcile deferred annotations."
-        )  # pragma: no cover
-
     session_method = getattr(bigframes.session.Session, method_name)
     session_doc = inspect.getdoc(session_method)
     assert session_doc is not None, "docstrings are required"