Python: AttributeError: Can't pickle local object 'writeBuf.<locals>.write'

I am not at all familiar with Python, I usually do Ruby or JS. But I need to write a benchmarking script on a system that runs Python. What I'm trying to do is create a small script that gets a file size and the number of threads and write a random buffer. This is what I got after 2 hours of fiddling:

from multiprocessing import Pool
import os, sys

def writeBuf(buf):
    def write(n):
        f = open(os.path.join(directory, 'n' + str(n)), 'w')
        try:
            f.write(buf)
            f.flush()
            os.fsync(f.fileno)
        finally:
            f.close()
    return write

if __name__ == '__main__':
    targetDir = sys.argv[1]
    numThreads = int(sys.argv[2])
    numKiloBytes = int(sys.argv[3])
    numFiles = int(102400 / numKiloBytes)

    buf = os.urandom(numKiloBytes * 1024)

    directory = os.path.join(targetDir, str(numKiloBytes) + 'k')
    if not os.path.exists(directory):
        os.makedirs(directory)

    with Pool(processes=numThreads) as pool:
        pool.map(writeBuf(buf), range(numFiles))

But it throws the error: AttributeError: Can't pickle local object 'writeBuf.<locals>.write'

I have tried before to use write without the closure, but I got an error when I tried to define the function inside the __name__ == '__main__' part. Omitting that if also lead to an error and I read that it is required for Pool to work.

What's supposed to be just a tiny script turned into a huge ordeal, can anyone point me the right way?