def leap_year(gyear):
    """Determine if this is a Gregorian leap year.

    Parameters
    ----------
    gyear : int
        Gregorian year.

    Returns
    -------
    leap_year : bool
        True if a Gregorian leap year, else False.
    """
    mod1 = gyear % 4 == 0
    mod2 = True
    if gyear % 100 == 0:
        mod2 = gyear % 400 == 0
    leap_year = False
    if mod1 and mod2:
        leap_year = True
    return leap_year
