How to reuse a selenium driver instance during parallel processing?

Question

To scrape a pool of URLs, I am paralell processing selenium with joblib. In this context, I am facing two challenges:

• Challenge 1 is to speed up this process. In t

Answer 1

1) You should first create a bunch of drivers: one for each process. And pass an instance to the worker. I don't know how to pass drivers to an Prallel object, but you could use threading.current_thread().name key to identify drivers. To do that, use backend="threading". So now each thread will has its own driver.

2) You don't need a loop at all. Parallel object itself iter all your urls (I hope I realy understend your intentions to use a loop)

import threading
from joblib import Parallel, delayed
from selenium import webdriver

def scrape(URL):
    try:
        driver = drivers[threading.current_thread().name]
    except KeyError:
        drivers[threading.current_thread().name] = webdriver.Firefox()
        driver = drivers[threading.current_thread().name]
    driver.get(URL)
    results = do_something(driver)
    if results:
        safe_results("results.csv")

drivers = {}
Parallel(n_jobs=-1, backend="threading")(delayed(scrape)(URL) for URL in URL_list)
for driver in drivers.values():
    driver.quit()

But I don't realy think you get profit in using n_job more than you have CPUs. So n_jobs=-1 is the best (of course I may be wrong, try it).