def leap_year(year):
    """leap_year returns True if *year* is a leap year and False otherwise.

    Note that leap years famously fall on all years that divide by 4
    except those that divide by 100 but including those that divide
    by 400."""
    if year % 4:            # doesn't divide by 4
        return False
    elif year % 100:        # doesn't divide by 100
        return True
    elif year % 400:        # doesn't divide by 400
        return False
    else:
        return True