I'd like to launch Chrome with its default profile using Python's webdriver so that cookies and site preferences persist across sessions.

How can I do that?

This is what finally got it working for me.

from selenium import webdriver

options = webdriver.ChromeOptions() 
options.add_argument("user-data-dir=C:\\Path") #Path to your chrome profile
w = webdriver.Chrome(executable_path="C:\\Users\\chromedriver.exe", chrome_options=options)

To find path to your chrome profile data you need to type chrome://version/ into address bar . For ex. mine is displayed as C:\Users\pc\AppData\Local\Google\Chrome\User Data\Default, to use it in the script I had to exclude \Default\ so we end up with only C:\Users\pc\AppData\Local\Google\Chrome\User Data.

Also if you want to have separate profile just for selenium: replace the path with any other path and if it doesn't exist on start up chrome will create new profile and directory for it.