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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 get_model_home():
    '''
    Returns a root folder path for downloading models.
    '''
    d = os.path.join(get_data_home(), 'nnp_models')
    if not os.path.isdir(d):
        os.makedirs(d)
    return d