如何在日期中减去年份并添加月份？

from datetime import datetime, timedelta

def subtract_year_and_add_month(date_str, year_to_subtract, month_to_add):
    # 将字符串转换为datetime对象
    date_obj = datetime.strptime(date_str, "%Y-%m-%d")

    # 减去指定的年份
    new_date = date_obj - timedelta(days=365*year_to_subtract)

    # 添加指定的月份
    month_to_add = month_to_add % 12
    year_to_add = new_date.year + (new_date.month + month_to_add - 1) // 12
    month = (new_date.month + month_to_add - 1) % 12 + 1
    day = min(new_date.day, [31, 29 if year_to_add % 4 == 0 and (year_to_add % 100 != 0 or year_to_add % 400 == 0) else 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31][month - 1])
    new_date = new_date.replace(year=year_to_add, month=month, day=day)

    return new_date.strftime("%Y-%m-%d")

date_str = "2021-08-15"  # 示例日期
year_to_subtract = 1  # 要减去的年数
month_to_add = 2  # 要添加的月数

new_date = subtract_year_and_add_month(date_str, year_to_subtract, month_to_add)
print(new_date)  # 输出结果: 2020-10-15