pythonマルチプロセスランニング関数

import multiprocessing

def calculation(num):
    for i in range(num):
        a = num + 3
        print(a)
        return a

if __name__ == '__main__':
    lists = [i for i in range(10000000)]
    cores = multiprocessing.cpu_count()
    print(cores)
    pool = multiprocessing.Pool(processes=cores)
    pool.map(calculation,lists)