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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 main(model=None, output_dir=None, n_iter=15):
 """Load the model, set up the pipeline and train the parser."""

    if model is not None:
        nlp = spacy.load(model)  # load existing spaCy model
        print("Loaded model '%s'" % model)
    else:
        nlp = spacy.blank("en")  # create blank Language class
        print("Created blank 'en' model")

    # We'll use the built-in dependency parser class, but we want to create a
    # fresh instance – just in case.
    if "parser" in nlp.pipe_names:
        nlp.remove_pipe("parser")
    parser = nlp.create_pipe("parser")
    nlp.add_pipe(parser, first=True)

    for text, annotations in TRAIN_DATA:
        for dep in annotations.get("deps", []):
            parser.add_label(dep)

    other_pipes = [pipe for pipe in nlp.pipe_names if pipe != "parser"]
    with nlp.disable_pipes(*other_pipes):  # only train parser
        optimizer = nlp.begin_training()
        for itn in range(n_iter):
            random.shuffle(TRAIN_DATA)
            losses = {}
            # batch up the examples using spaCy's minibatch
            batches = minibatch(TRAIN_DATA, size=compounding(4.0, 32.0, 1.001))
            for batch in batches:
                texts, annotations = zip(*batch)
                nlp.update(texts, annotations, sgd=optimizer, losses=losses)
            print("Losses", losses)

    # test the trained model
    test_model(nlp)

    # save model to output directory
    if output_dir is not None:
        output_dir = Path(output_dir)
        if not output_dir.exists():
            output_dir.mkdir()
        nlp.to_disk(output_dir)
        print("Saved model to", output_dir)

        # test the saved model
        print("Loading from", output_dir)
        nlp2 = spacy.load(output_dir)
        test_model(nlp2)