from selenium import webdriver
user_agent = 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.50 Safari/537.36'
options = webdriver.ChromeOptions()
# specify headless mode
options.add_argument('headless')
# specify the desired user agent
options.add_argument(f'user-agent={user_agent}')
driver = webdriver.Chrome(chrome_options=options)
# user-agent is now set