我如何在我的程序中计算年差？

import datetime

def calculate_year_difference(current_date, target_date):
    current_year = current_date.year
    target_year = target_date.year

    # 计算年份差
    year_difference = current_year - target_year

    # 考虑闰年
    leap_years = 0
    for year in range(target_year, current_year):
        if (year % 4 == 0 and year % 100 != 0) or year % 400 == 0:
            leap_years += 1

    year_difference += leap_years

    # 处理边界情况
    if current_date.month < target_date.month or (current_date.month == target_date.month and current_date.day < target_date.day):
        year_difference -= 1

    return year_difference

# 示例用法
current_date = datetime.datetime.now()
target_date = datetime.datetime(2018, 6, 15)
year_difference = calculate_year_difference(current_date, target_date)
print("年差：", year_difference)