Am using Python 3.6.5rcs , pip version 9.0.1 , selenium 3.11.0. The Python is installed in C:\Python and selenium is in C:\Python\Lib\site-packages\selenium. The environment variables have been set. 
But the code
from selenium import webdriver
gives an unresolved reference error.
Any suggestion on how to fix the problem.
I found this worked for me. I'm using PyCharm Community 2018.1.4 on Windows.
Navigate to: File->Settings->Project: [project name] -> Project Interpreter
On this page click the configuration wheel at the top which should provide a drop down menu. Click "Add" and a window should appear called "Add Python Interpreter"
You will be defaulted onto "Virtualenv Environment" tab.
There should be a checkbox called "Inherit global site-packages". Check this.
Click OK.
All your installed packages should be added.
Pycharm Referenced Error With Import Selenium Webdriver