Generate an equally-spaced sequence of cftime.datetime objects between
    and including two dates (whose length equals the number of periods).

def _generate_linear_range(start, end, periods):
    """Generate an equally-spaced sequence of cftime.datetime objects between
    and including two dates (whose length equals the number of periods)."""
    import cftime

    total_seconds = (end - start).total_seconds()
    values = np.linspace(0., total_seconds, periods, endpoint=True)
    units = 'seconds since {}'.format(format_cftime_datetime(start))
    calendar = start.calendar
    return cftime.num2date(values, units=units, calendar=calendar,
                           only_use_cftime_datetimes=True)