Determine if a year is leap year.

    Parameters
    ----------
    year : numeric

    Returns
    -------
    isleap : array of bools

def _is_leap_year(year):
    """Determine if a year is leap year.

    Parameters
    ----------
    year : numeric

    Returns
    -------
    isleap : array of bools
    """
    isleap = ((np.mod(year, 4) == 0) &
              ((np.mod(year, 100) != 0) | (np.mod(year, 400) == 0)))
    return isleap