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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def call_learn_bpe(workspace_dir: str, source_fname: str, target_fname: str, model_fname: str, num_ops: int = 32000):
 """ Call script to learn byte-pair encoding model. :param workspace_dir: Workspace third-party directory where subword-nmt is checked out. :param source_fname: Path of source corpus file, plain text or gzipped. :param target_fname: Path of target corpus file, plain text or gzipped. :param model_fname: Path to write out model. :param num_ops: Number of operations. """

    learn_bpe_fname = os.path.join(workspace_dir, DIR_THIRD_PARTY, SUBWORD_NMT_DEST, "learn_bpe.py")
    with bin_open(source_fname) as src_in, bin_open(target_fname) as trg_in, open(model_fname, "wb") as out:
        learn_bpe = subprocess.Popen([sys.executable, learn_bpe_fname, "-s", str(num_ops)],
                                     stdin=subprocess.PIPE,
                                     stdout=subprocess.PIPE)
        learn_bpe_thread = threading.Thread(target=copy_out, args=(learn_bpe.stdout, out))
        learn_bpe_thread.start()
        for inp in (src_in, trg_in):
            for line in inp:
                learn_bpe.stdin.write(line)
        learn_bpe.stdin.close()
        learn_bpe_thread.join()
        learn_bpe.wait()