def _pretty_time_delta(td):
    """Creates a string representation of a time delta.

    Parameters
    ----------
    td : :class:`datetime.timedelta`

    Returns
    -------
    pretty_formatted_datetime : str
    """
    seconds = td.total_seconds()
    sign_string = '-' if seconds < 0 else ''
    seconds = abs(int(seconds))
    days, seconds = divmod(seconds, 86400)
    hours, seconds = divmod(seconds, 3600)
    minutes, seconds = divmod(seconds, 60)
    d = dict(sign=sign_string, days=days, hours=hours, minutes=minutes, seconds=seconds)
    if days > 0:
        return '{sign}{days}d{hours:02d}h{minutes:02d}m:{seconds:02d}s'.format(**d)
    elif hours > 0:
        return '{sign}{hours:02d}h{minutes:02d}m:{seconds:02d}s'.format(**d)
    elif minutes > 0:
        return '{sign}{minutes:02d}m:{seconds:02d}s'.format(**d)
    else:
        return '{sign}{seconds:02d}s'.format(**d)
Creates a string representation of a time delta.

    Parameters
    ----------
    td : :class:`datetime.timedelta`

    Returns
    -------
    pretty_formatted_datetime : str