Quick and easy Python concurrency

This post serves as a simple reminder to myself that multiprocessing.Pool has map and starmap functions that are a quick and easy way to take a loop and parallelise it in Python.

Imagine some code like this:

urls = ["https://example.org",]

def take_screenshot(url):
    # ...

for url in urls:
    take_screenshot(url)

To make this run across four separate processes, you can do this:

pool = multiprocessing.Pool(4)
pool.map(take_screenshot, urls)

Where does starmap come into it? Well, it lets you invoke the function with multiple arguments by expanding the list you pass in.

urls = [
    ("https://example.org", "example.png")
]

def take_screenshot(url, filename):
    # ...

pool = multiprocessing.Pool(4)
pool.starmap(take_screenshot, urls)

This is super handy for quick scripts, but as always there's trade-offs here. Check out this more detailed post to see other ways of managing concurrency in Python.