ThreadPoolExecutor read file to list

[DeaD_EyE]

The Python Documentation shows a good example: threadpoolexecutor-example
If you use this as example and replace the load_url function with read_file it could work like this:

import time
from random import randint, choice
from concurrent.futures import (
    ThreadPoolExecutor,
    as_completed,
    )


def computation(desc):
    print('Slow task', desc)
    pause = randint(1,10)
    time.sleep(pause)
    return desc


def read_file(file):
    # simulation of big file
    computation('reading ' + file)
    if choice([True, False]):
        exc = choice([ZeroDivisionError('Not really'), ValueError('Wrong input'), TypeError('Wrong operation')])
        raise exc
    with open(file) as fd:
        return fd.read()

############
files = ('Chesterton.txt', 'Alice.txt', 'Chesterton.txt', 'Alice.txt', 'Chesterton.txt', 'Alice.txt')
############

# We can use a with statement to ensure threads are cleaned up promptly
with ThreadPoolExecutor(max_workers=5) as executor:
    # Start the load operations and mark each future with its file
    future_to_text = {executor.submit(read_file, file): file for file in files} # <- this is a dict
    # alternative
    # future_to_text = {}
    # for file in files:
    #     future = executor.submit(read_file, file)
    #     future_to_text[future] = file
    #
    # they keys are the futures, the values are the filenames
    for future in as_completed(future_to_text):
        # iterating over a dict directly, returns the key, in this case the futures
        # as_completed returns the future, as it's as_completed, it may out of order
        file = future_to_text[future]
        # text is the future
        try:
            data = future.result()
        except Exception as exc:
            print(f'{file!r} generated an exception: {exc!r}')
        else:
            print(f'{file!r} is {len(data)} chars long')