TypeError：+不支持的操作数类型：“ generator”和“ generator” [英] TypeError: unsupported operand type(s) for +: 'generator' and 'generator'

问题描述

我在目标函数中添加三个表达式时遇到问题。我使用 quicksum 构建每个表达式。但是，当我尝试将它们加在一起时，出现一个错误，我无法在类'generator'上使用+/-操作数。

I have a problem with adding three expressions in my objective function. I used quicksum to build each expression. However, when I try to add them together I get an error that I cannot use +/- operands on class 'generator'.

这是我代码的最后一部分：

Here is the last part of my code:

# the shipping cost expression
expr_sc = []
for j in J:
    for k in K:
        expr_sc.append(quicksum(r_jk[(j, k)]*x[(i, j, k)]) for i in I)

m.setObjective((quicksum(item_rev) for item_rev in expr_rev) -
               ((quicksum(item_pc) for item_pc in expr_pc) + (quicksum(item_sc) for item_sc in expr_sc)),
               GRB.MAXIMIZE)

更新：

此处为实际值我要解决的问题：
目标函数
问题是我不知道如何在Gurobi Python中编写该表达式！

Update:

here is the actual problem that I am trying to solve: Objective Function The problem is I don't know how to write this expression in Gurobi Python!!

推荐答案

（ expr_rev中item_rev的quicksum（item_rev）计算为生成器expre ssion。

(quicksum(item_rev) for item_rev in expr_rev) evaluates to a generator expression.

如果 for 循环的一行位于括号内-（...） -您将获得一个生成器对象。这是一个小例子，说明我的意思：

If the one line for loop is inside the parenthesis - (...) - you get a generator object. Here's a small example to illustrate what I mean:

>>> (x for x in range(5)) # shorthand for creating generators
<generator object <genexpr> at 0xb74308ec>

请参见文档了解更多信息。

似乎您正在尝试将给定列表中的单个项目传递给 quicksum ，但您是无意中创建了生成器。

It seems you're trying to pass individual items from given lists to quicksum, but instead you're creating generators, unintentionally.

要解决此错误，请将对象直接传递到 quicksum ：

To fix this error, directly pass the objects to quicksum:

m.setObjective(
    quicksum(expr_rev) - (quicksum(expr_pc) + quicksum(expr_sc)),
    GRB.MAXIMIZE
)

更新：

似乎也有问题在

expr_sc.append(quicksum(r_jk[(j, k)]*x[(i, j, k)]) for i in I)

像这样更改该行：

expr_sc.append(quicksum(r_jk[(j, k)] * x[(i, j, k)] for i in I))

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