债券久期

def solve(____):
    coupon = face_value * coupon_rate
    price = sum(coupon / (____ + ytm) ** t for t in range(____, maturity + ____))
    price += face_value / (____ + ytm) ** maturity
    weighted_time = sum(t * coupon / (____ + ytm) ** t for t in range(____, maturity + ____))
    weighted_time += maturity * face_value / (____ + ytm) ** maturity
    duration = weighted_time / price
    return {"____": round(____), "____": round(____), "____": round(duration / (____ + ytm), ____)}