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

    Parameters
    ----------
    text : str
        Text from vw file.

    Returns
    -------
    dict of (str, float)
        Dictionary with field "average_loss", lower bound on mean per-word log-perplexity.

    """
    data = {}
    for line in text.splitlines():
        if line.startswith('average loss'):
            data['average_loss'] = float(line.split('=')[1])
            break
    return data
