feat: require python >= 3.6 (#674)

We are not ready to require >=3.6 in the main branch, so I am opening this PR against a new `2.0.0dev` branch. For googleapis/gapic-generator#3334 (comment)

Use native namespaces (delete `google/__init__.py` and require python>=3.6).

There is more cleanup that needs to happen (example: App Engine credentials) in future PRs.

google/auth/jwt.py

@@ -40,11 +40,7 @@
 
 """
 
-try:
-    from collections.abc import Mapping
-# Python 2.7 compatibility
-except ImportError:  # pragma: NO COVER
-    from collections import Mapping
+from collections.abc import Mapping
 import copy
 import datetime
 import json

noxfile.py

@@ -90,15 +90,6 @@ def unit(session):
     )
 
 
-@nox.session(python=["2.7"])
-def unit_prev_versions(session):
-    session.install(*TEST_DEPENDENCIES)
-    session.install(".")
-    session.run(
-        "pytest", "--cov=google.auth", "--cov=google.oauth2", "--cov=tests", "tests"
-    )
-
-
 @nox.session(python="3.7")
 def cover(session):
     session.install(*TEST_DEPENDENCIES)

setup.py

@@ -14,27 +14,30 @@
 
 import io
 
-from setuptools import find_packages
+from setuptools import PEP420PackageFinder
 from setuptools import setup
 
 
 DEPENDENCIES = (
     "cachetools>=2.0.0,<5.0",
     "pyasn1-modules>=0.2.1",
-    # rsa==4.5 is the last version to support 2.7
-    # https://github.com/sybrenstuvel/python-rsa/issues/152#issuecomment-643470233
-    'rsa<4.6; python_version < "3.6"',
-    'rsa>=3.1.4,<5; python_version >= "3.6"',
+    "rsa>=3.1.4,<5",
     "setuptools>=40.3.0",
     "six>=1.9.0",
 )
 
-extras = {"aiohttp": "aiohttp >= 3.6.2, < 4.0.0dev; python_version>='3.6'"}
+extras = {"aiohttp": "aiohttp >= 3.6.2, < 4.0.0dev"}
 
 with io.open("README.rst", "r") as fh:
     long_description = fh.read()
 
-version = "1.24.0"
+version = "2.0.0dev"
+
+# Only include packages under the 'google' namespace. Do not include tests,
+# benchmarks, etc.
+packages = [
+    package for package in PEP420PackageFinder.find() if package.startswith("google")
+]
 
 setup(
     name="google-auth",
@@ -44,16 +47,13 @@
     description="Google Authentication Library",
     long_description=long_description,
     url="https://github.com/googleapis/google-auth-library-python",
-    packages=find_packages(exclude=("tests*", "system_tests*")),
-    namespace_packages=("google",),
+    packages=packages,
     install_requires=DEPENDENCIES,
     extras_require=extras,
-    python_requires=">=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*",
+    python_requires=">=3.6",
     license="Apache 2.0",
     keywords="google auth oauth client",
     classifiers=[
-        "Programming Language :: Python :: 2",
-        "Programming Language :: Python :: 2.7",
         "Programming Language :: Python :: 3",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",

system_tests/noxfile.py

@@ -171,7 +171,7 @@ def configure_cloud_sdk(session, application_default_credentials, project=False)
 TEST_DEPENDENCIES_ASYNC = ["aiohttp", "pytest-asyncio", "nest-asyncio"]
 TEST_DEPENDENCIES_SYNC = ["pytest", "requests", "mock"]
 PYTHON_VERSIONS_ASYNC = ["3.7"]
-PYTHON_VERSIONS_SYNC = ["2.7", "3.7"]
+PYTHON_VERSIONS_SYNC = ["3.7"]
 
 
 @nox.session(python=PYTHON_VERSIONS_SYNC)
@@ -242,49 +242,6 @@ def compute_engine(session):
     session.install(LIBRARY_DIR)
     session.run("pytest", "system_tests_sync/test_compute_engine.py")
 
-
-@nox.session(python=["2.7"])
-def app_engine(session):
-    if SKIP_GAE_TEST_ENV in os.environ:
-        session.log("Skipping App Engine tests.")
-        return
-
-    session.install(LIBRARY_DIR)
-    # Unlike the default tests above, the App Engine system test require a
-    # 'real' gcloud sdk installation that is configured to deploy to an
-    # app engine project.
-    # Grab the project ID from the cloud sdk.
-    project_id = (
-        subprocess.check_output(
-            ["gcloud", "config", "list", "project", "--format", "value(core.project)"]
-        )
-        .decode("utf-8")
-        .strip()
-    )
-
-    if not project_id:
-        session.error(
-            "The Cloud SDK must be installed and configured to deploy to App " "Engine."
-        )
-
-    application_url = GAE_APP_URL_TMPL.format(GAE_TEST_APP_SERVICE, project_id)
-
-    # Vendor in the test application's dependencies
-    session.chdir(os.path.join(HERE, "system_tests_sync/app_engine_test_app"))
-    session.install(*TEST_DEPENDENCIES_SYNC)
-    session.run(
-        "pip", "install", "--target", "lib", "-r", "requirements.txt", silent=True
-    )
-
-    # Deploy the application.
-    session.run("gcloud", "app", "deploy", "-q", "app.yaml")
-
-    # Run the tests
-    session.env["TEST_APP_URL"] = application_url
-    session.chdir(HERE)
-    session.run("pytest", "system_tests_sync/test_app_engine.py")
-
-
 @nox.session(python=PYTHON_VERSIONS_SYNC)
 def grpc(session):
     session.install(LIBRARY_DIR)