DouKaku?

>>> def leap(x, d=400):
    if x < 0:
        return leap(-x, d)

    if x == 0:
        if d == 400:
            return True
        if d == 100:
            return False
        if d == 4:
            return True

    if x < d:
        if d == 400:
            return leap(x, 100)
        if d == 100:
            return leap(x, 4)
        if d == 4:
            return False

    return leap(x - d, d)

>>> leap(1900)
False
>>> leap(2000)
True
>>> leap(2008)
True
>>> leap(2100)
False