Find sum by using common Aggregator

MultiThread.py

import concurrent.futures
import threading

a=0
def fn(i):
    global a
    a=a+i
    print(a,threading.get_native_id())

if __name__ == '__main__':
    with concurrent.futures.ThreadPoolExecutor(3) as ep:
        ep.map(fn, range(0, 100))
    print("final " + str(a))