In Python, how to check if Selenium WebDriver has quit or not?

be Pythonic... try to quit and catch the exception if it fails.

try:
    driver.quit()
except WebDriverException:
    pass

You can use something like this which uses psutil

from selenium import webdriver
import psutil

driver = webdriver.Firefox()

driver.get("http://tarunlalwani.com")

driver_process = psutil.Process(driver.service.process.pid)

if driver_process.is_running():
    print ("driver is running")

    firefox_process = driver_process.children()
    if firefox_process:
        firefox_process = firefox_process[0]

        if firefox_process.is_running():
            print("Firefox is still running, we can quit")
            driver.quit()
        else:
            print("Firefox is dead, can't quit. Let's kill the driver")
            firefox_process.kill()
    else:
        print("driver has died")

This is what I figured out and liked:

def setup(self):
    self.wd = webdriver.Firefox()

def teardown(self):
    # self.wd.service.process == None if quit already.
    if self.wd.service.process != None:
        self.wd.quit()

Note: driver_process=psutil.Process(driver.service.process.pid) will throw exception if driver already quits.

The answer by Corey Golberg is the correct way.

However if you really need to look under the hood, the driver.service.process property gives access to the underlying Popen object that manages the open browser. If the process has quit, the process property will be None and testing whether it is truthy will identify the state of the browser:

from selenium import webdriver
driver = webdriver.Firefox()

# your code where the browser quits

if not driver.service.process:
    print('Browser has quit unexpectedly')

if driver.service.process:
    driver.quit()