How does ThreadPoolExecutor().map differ from ThreadPoolExecutor().submit?

Question

I was just very confused by some code that I wrote. I was surprised to discover that:

with concurrent.futures.ThreadPoolExecutor(max_workers=4) as executor:
             


        

Answer 1

if you use concurrent.futures.as_completed, you can handle the exception for each function.

import concurrent.futures
iterable = [1,2,3,4,6,7,8,9,10]

def f(x):
    if x == 2:
        raise Exception('x')
    return x

with concurrent.futures.ThreadPoolExecutor(max_workers=4) as executor:
    result_futures = list(map(lambda x: executor.submit(f, x), iterable))
    for future in concurrent.futures.as_completed(result_futures):
        try:
            print('resutl is', future.result())
        except Exception as e:
            print('e is', e, type(e))
# resutl is 3
# resutl is 1
# resutl is 4
# e is x 
# resutl is 6
# resutl is 7
# resutl is 8
# resutl is 9
# resutl is 10

in executor.map, if there is an exception, the whole executor would stop. you need to handle the exception in the worker function.

with concurrent.futures.ThreadPoolExecutor(max_workers=4) as executor:
    for each in executor.map(f, iterable):
        print(each)
# if there is any exception, executor.map would stop