def _parse_vw_output(text):
    """Get dict of useful fields from Vowpal Wabbit's output.

    Currently returns field 'average_loss', which is a lower bound on mean
    per-word log-perplexity (i.e. same as the value LdaModel.bound() returns).
    """
    data = {}
    for line in text.splitlines():
        if line.startswith('average loss'):
            data['average_loss'] = float(line.split('=')[1])
            break

    return data