QuantLib :如何计算修改后的债券存续期？

import QuantLib as ql

# 创建债券对象
face_value = 100  # 面值
coupon_rate = 0.05  # 利率
maturity_date = ql.Date(31, 12, 2022)  # 到期日
issue_date = ql.Date(1, 1, 2020)  # 发行日
payment_frequency = ql.Semiannual  # 付息频率

bond = ql.FixedRateBond(2, ql.TARGET(), face_value, issue_date, maturity_date, ql.Period(payment_frequency), [coupon_rate], ql.ActualActual())

# 计算下一次付息日期
calendar = bond.calendar()
settlement_days = bond.settlementDays()
settlement_date = calendar.advance(ql.Date.todaysDate(), settlement_days, ql.Days)
next_payment_date = bond.nextCouponDate(settlement_date)

# 设置下一次付息日期来修改债券存续期
bond.setSingleRedemption(next_payment_date)

# 打印修改后的债券存续期
print("修改后的债券存续期：", bond.maturityDate().serialNumber() - ql.Date.todaysDate().serialNumber(), "天")