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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 load_sst(path=None, url='http://nlp.stanford.edu/sentiment/trainDevTestTrees_PTB.zip'):
 """ Download and read in the Stanford Sentiment Treebank dataset into a dictionary with a 'train', 'dev', and 'test' keys. The dictionary keys point to lists of LabeledTrees. Arguments: path : str, (optional defaults to ~/stanford_sentiment_treebank), directory where the corpus should be downloaded (and imported from). url : str, where the corpus should be downloaded from (defaults to nlp.stanford.edu address). Returns: -------- dict : loaded dataset """

    if path is None:
        # find a good temporary path
        path = os.path.expanduser("~/stanford_sentiment_treebank/")
        makedirs(path, exist_ok=True)
    fnames = download_sst(path, url)
    return {key: import_tree_corpus(value) for key, value in fnames.items()}