12.3.10.5.2. Thread pool executor

Asyncio/concurrent heavily changed from python 3.4 to 3.7, better read the docs and do some tutorials. Asyncio is preferred over plain concurrent module.

import concurrent.futures
import urllib.request

URLS = [
    "http://www.foxnews.com/",
    "http://www.cnn.com/",
    "http://europe.wsj.com/",
    "http://www.bbc.co.uk/",
    "http://some-made-up-domain.com/",
]

Retrieve a single page and report the url and contents

def load_url(url, timeout):
    with urllib.request.urlopen(url, timeout=timeout) as conn:
        return conn.read()

We can use a with statement to ensure threads are cleaned up promptly

with concurrent.futures.ThreadPoolExecutor(max_workers=5) as executor:
    # Start the load operations and mark each future with its URL
    future_to_url = {executor.submit(load_url, url, 60): url for url in URLS}
    for future in concurrent.futures.as_completed(future_to_url):
        url = future_to_url[future]
        try:
            data = future.result()
        except Exception as exc:
            print(f"{url!r} generated an exception: {exc}")
        else:
            print("%r page is %d bytes" % (url, len(data)))

'http://www.foxnews.com/' page is 718244 bytes
'http://europe.wsj.com/' generated an exception: HTTP Error 403: Forbidden
'http://www.cnn.com/' page is 3063439 bytes
'http://www.bbc.co.uk/' page is 557992 bytes
'http://some-made-up-domain.com/' generated an exception: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1000)>