BREAKING CHANGE: Drop support for Python 2.7

Per the readme, Python 2.7 support was to be dropped on January 1, 2020.
This lays the groundwork for making it easier to drop the dependency on
pytz.

Author: pganssle

CONTRIBUTING.rst

@@ -21,7 +21,7 @@ In order to add a feature:
 - The feature must be documented in both the API and narrative
   documentation.
 
-- The feature must work fully on the following CPython versions:  2.7,
+- The feature must work fully on the following CPython versions:
   3.5, 3.6, 3.7 and 3.8 on both UNIX and Windows.
 
 - The feature must not add unnecessary dependencies (where
@@ -69,7 +69,6 @@ We use `nox <https://nox.readthedocs.io/en/latest/>`__ to instrument our tests.
 
 - To test your changes, run unit tests with ``nox``::
 
-    $ nox -s unit-2.7
     $ nox -s unit-3.7
     $ ...
 
@@ -143,13 +142,11 @@ Running System Tests
 - To run system tests, you can execute::
 
    $ nox -s system-3.7
-   $ nox -s system-2.7
 
   .. note::
 
-      System tests are only configured to run under Python 2.7 and
-      Python 3.7. For expediency, we do not run them in older versions
-      of Python 3.
+      System tests are only configured to run under Python 3.7. For expediency,
+      we do not run them in older versions.
 
   This alone will not run the tests. You'll need to change some local
   auth settings and change some configuration in your project to
@@ -226,8 +223,6 @@ Supported versions can be found in our ``noxfile.py`` `config`_.
 
 .. _config: https://github.com/googleapis/python-api-core/blob/master/noxfile.py
 
-Python 2.7 support is deprecated. All code changes should maintain Python 2.7 compatibility until January 1, 2020.
-
 We also explicitly decided to support Python 3 beginning with version
 3.5. Reasons for this include:
 

README.rst

@@ -17,7 +17,3 @@ common helpers used by all Google API clients. For more information, see the
 Supported Python Versions
 -------------------------
 Python >= 3.5
-
-Deprecated Python Versions
---------------------------
-Python == 2.7. Python 2.7 support will be removed on January 1, 2020.

noxfile.py

@@ -72,13 +72,13 @@ def default(session):
         session.run(*pytest_args)
 
 
-@nox.session(python=["2.7", "3.5", "3.6", "3.7", "3.8"])
+@nox.session(python=["3.5", "3.6", "3.7", "3.8"])
 def unit(session):
     """Run the unit test suite."""
     default(session)
 
 
-@nox.session(python=["2.7", "3.5", "3.6", "3.7", "3.8"])
+@nox.session(python=["3.5", "3.6", "3.7", "3.8"])
 def unit_grpc_gcp(session):
     """Run the unit test suite with grpcio-gcp installed."""
 
@@ -108,7 +108,6 @@ def lint_setup_py(session):
     session.run("python", "setup.py", "check", "--restructuredtext", "--strict")
 
 
-# No 2.7 due to https://github.com/google/importlab/issues/26.
 # No 3.7 because pytype supports up to 3.6 only.
 @nox.session(python="3.6")
 def pytype(session):

setup.py

@@ -79,12 +79,12 @@
         "Intended Audience :: Developers",
         "License :: OSI Approved :: Apache Software License",
         "Programming Language :: Python",
-        "Programming Language :: Python :: 2",
-        "Programming Language :: Python :: 2.7",
         "Programming Language :: Python :: 3",
         "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
         "Operating System :: OS Independent",
         "Topic :: Internet",
     ],
@@ -93,7 +93,7 @@
     namespace_packages=namespaces,
     install_requires=dependencies,
     extras_require=extras,
-    python_requires=">=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*",
+    python_requires=">=3.5",
     include_package_data=True,
     zip_safe=False,
 )