Modern Python Standard Library Cookbook

How it works...

UrlsBenchmarker will fire a future for each URL through UrlsBenchmarker._benchmark_urls:

for url in self._urls:
    future = executor.submit(benchmark_url, url)

Each future will perform benchmark_url, which downloads the content of the given URL and returns the time it took to download it, along with the URL itself:

def benchmark_url(url):
    begin = time.time()
    # download url here...
    return (time.time() - begin, url)

Returning the URL itself is necessary, as future can know its return value, but not its arguments. So once we submit the function, we have lost which URL it is related to and by returning it together with the timing, we will always have the URL available whenever the timing is present.

Then for each future, a callback ...