如何在pyomo抽象模型中实例化带索引的块？

from pyomo.environ import *

model = AbstractModel()

model.index_set = Set()
model.block = Block(model.index_set)

@model.block.block()
def my_block(b, i):
    b.x = Var()
    b.y = Var()
    b.c = Constraint(expr=b.x + b.y <= 1)
    b.obj = Objective(expr=b.x + 2*b.y)

instance = model.create_instance(data={'index_set': [1, 2, 3]})

instance.block[1].x = 0.5
print(value(instance.block[1].x))  # 获取变量x的值
print(instance.block[1].c.body())  # 获取约束c的表达式
print(instance.block[1].obj.expr)  # 获取目标函数obj的表达式