address review comments

Author: busunkim96

README.md

@@ -48,8 +48,11 @@ virtualenv <your-env>
 
 ## Supported Python Versions
 
-Python 3.5, 3.6 and 3.7, and 3.8 are fully supported and tested. This library may work on later versions of 3, but we do not currently run tests against those versions
+Python 3.6 and 3.7, and 3.8 are fully supported and tested. This library may work on later versions of 3, but we do not currently run tests against those versions
 
+## Unsupported Python Versions	
+
+Python == 2.7
 
 ## Third Party Libraries and Dependencies
 

setup.py

@@ -19,6 +19,15 @@
 """
 from __future__ import print_function
 
+import sys
+
+if sys.version_info < (2, 7):
+    print("google-api-python-client requires python version >= 2.7.", file=sys.stderr)
+    sys.exit(1)
+if (3, 1) <= sys.version_info < (3, 6):
+    print("google-api-python-client requires python3 version >= 3.6.", file=sys.stderr)
+    sys.exit(1)
+
 import io
 import os
 from setuptools import setup
@@ -52,14 +61,13 @@
     author_email="[email protected]",
     url="https://github.com/googleapis/google-api-python-client/",
     install_requires=install_requires,
-    python_requires=">=3.5",
+    python_requires=">=3.6",
     packages=packages,
     package_data={},
     license="Apache 2.0",
     keywords="google api client",
     classifiers=[
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",