def errorBarType(ds):
    """Return type of error bars in list of datasets.
    'none', 'symmetric', 'asymmetric'
    """
    symerr = False
    for d in ds:
        if d.serr is not None:
            symerr = True
        elif d.perr is not None or d.nerr is not None:
            return 'asymmetric'
    if symerr:
        return 'symmetric'
    return 'none'
