Modern Python Standard Library Cookbook

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ThreadPool is particularly convenient when you have multiple entries to which you need to apply the same operation over and over. Suppose you have a list of four URLs that you need to download:

urls = [
    "https://httpbin.org/delay/1",
    "https://httpbin.org/delay/2",
    "https://httpbin.org/delay/3",
    "https://httpbin.org/delay/4"
]

Fetching them in a single thread would take a lot of time:

def fetch_all_urls():
    contents = []
    for url in urls:
        contents.append(fetch_url(url))
    return contents

We can test the time by running the function through the timeit module:

>>> import timeit
>>> timeit.timeit(fetch_all_urls, number=1)
12.116707602981478

If we could do so using a separate thread for each function, it would only take the time of ...