def timedelta_to_days(td):
    """
    Convert a `datetime.timedelta` object to a total number of days.

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

    Returns
    -------
    days : float
        Total number of days in the `datetime.timedelta` object.

    Examples
    --------
    >>> td = datetime.timedelta(4.5)
    >>> td
    datetime.timedelta(4, 43200)
    >>> timedelta_to_days(td)
    4.5

    """
    seconds_in_day = 24. * 3600.

    days = td.days + (td.seconds + (td.microseconds * 10.e6)) / seconds_in_day

    return days