Thanks for your reply, I have tried it but it did nothing. I implement it just like this:
#set cpu affinity
    pid = 0
    affinity_mask = {i for i in range(128)}
    os.sched_setaffinity(0, affinity_mask)
    print("Number of CPUs:", os.cpu_count())
    affinity = os.sched_getaffinity(pid)
    real_pid = os.getpid()
    print("Now, process {} is eligibl to run on:{}".format(real_pid,affinity))

In fact, It did print the process is eligible to run on CPU:0~127
Now, process 34094  is eligibl to run on:{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127}

However,when I use ps -eLF to check the threads of this process, it still uses the half of the CPU cores.
I set this environment export OMP_DISPLAY_ENV=true and then the script print the OpenMP message twice.Do you know what are the OpenMP calls in there two places?
As shown above,the first time OMP_PLACES is 0-127,but the second time it becomes 0-63.
If I do not use DDP and just execute the py script,then I found there is just one OpenMP message.