PythonExtensionChrome.py

from selenium import webdriver
from selenium.webdriver.common.keys import Keys
from selenium.webdriver.common.desired_capabilities import DesiredCapabilities
import time
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.common.by import By
from selenium.webdriver.chrome.options import Options

***** Chrome Options to add extensions *********
chop = webdriver.ChromeOptions()
chop.add_extension('/Path to your exetension.crx')
cc = chop.to_capabilities()
extension_var = cc['chromeOptions']['extensions']

******* Creating WebDriver instance ************

desired_cap={ 'browser': 'Chrome', 'browser_version': '47.0', 'os': 'Windows', 'os_version': '7','chromeOptions': {'args':[],'extensions':extension_var}}
driver = webdriver.Remote(
    command_executor='http://<username>:<access_key>@hub.browserstack.com:80/wd/hub',
    desired_capabilities=desired_cap 
 )

************** Code Logic *******
driver.get('http://www.google.com')
print driver.title
driver.quit()