Parallel copy of a single file

copy.py

import threading
import os
import sys

BLOCK_SIZE = 1024*1024
THREADS = 16

def write_range(source, target, start, amount, block_size):
    with open(source, 'r') as source_file:
        with open(target, 'r+') as target_file:
            source_file.seek(start)
            target_file.seek(start)
            for _block_num in xrange(amount / block_size):
                target_file.write(source_file.read(block_size))
            target_file.write(source_file.read(amount % block_size))

def main(source, target, threads_count=THREADS, block_size=BLOCK_SIZE):
    threads = []
    file_size = os.stat(source).st_size
    print '{} => {}, using {} threads, block size {}'.format(source, target, threads_count, block_size)
    with open(target, 'a') as target_file:
        pass
    for i in xrange(threads_count):
        args = (source, target, i * file_size/threads_count, file_size/threads_count, block_size)
        #print 'thread:', i, args
        t = threading.Thread(target=write_range, args=args)
        threads.append(t)
        t.start()

    for t in threads:
        t.join()

if __name__ == '__main__':
    main(*sys.argv[1:], threads_count=THREADS, block_size=BLOCK_SIZE)