python - Pulp (Python) 值错误 : need more than 1 value to unpack

Question

我正在尝试解决这个问题 http://www.me.utexas.edu/~jensen/ORMM/models/unit/linear/subunits/workforce/在 Python 上使用 PuLP。

这是我的代码:

from pulp import *

# Create the 'prob' variable to contain the problem data
prob = LpProblem("The Bus Problem",LpMinimize)

# The variables are created with a lower limit of zero
x0=LpVariable("Number of drivers at time 0",0,None,LpInteger)
x4=LpVariable("Number of drivers at time 4",0)
x8=LpVariable("Number of drivers at time 8",0)
x12=LpVariable("Number of drivers at time 12",0)
x16=LpVariable("Number of drivers at time 16",0)
x20=LpVariable("Number of drivers at time 20",0)

# The objective function is added to 'prob' first
prob += x0 + x4 + x8 + x12 + x16 + x20, "drivers"

# The five constraints are entered
prob += x0 + x4 >= 8, 
prob += x4 + x8 >= 10, 
prob += x8 + x12 >= 7, 
prob += x12 + x16 >= 12,
prob += x16 + x20 >= 4,

# The problem data is written to an .lp file
prob.writeLP("BusModel.lp")

# The problem is solved using PuLP's choice of Solver
prob.solve()

但是，当我运行它时，出现错误:

File "C:\Users___\Anaconda2\lib\site-packages\pulp\pulp.py", line 1337, in iadd other, name = other

ValueError: need more than 1 value to unpack

当我查看 pulp.py 时，代码中是这样写的:

def __iadd__(self, other):
        if isinstance(other, tuple):
            other, name = other
        else:
            name = None
        if other is True:
            return self
        if isinstance(other, LpConstraintVar):
            self.addConstraint(other.constraint)
        elif isinstance(other, LpConstraint):
            self.addConstraint(other, name)
        elif isinstance(other, LpAffineExpression):
            if self.objective is not None:
                warnings.warn("Overwriting previously set objective.")
            self.objective = other
            self.objective.name = name
        elif isinstance(other, LpVariable) or isinstance(other, (int, float)):
            if self.objective is not None:
                warnings.warn("Overwriting previously set objective.")
            self.objective = LpAffineExpression(other)
            self.objective.name = name
        else:
            raise TypeError("Can only add LpConstraintVar, LpConstraint, LpAffineExpression or True objects")
        return self

谁能看出任何明显的问题？谢谢!

Answer 1

您要在此处添加单元素元组:

prob += x0 + x4 >= 8, 
prob += x4 + x8 >= 10, 
prob += x8 + x12 >= 7, 
prob += x12 + x16 >= 12,
prob += x16 + x20 >= 4,

逗号使每个表达式成为一个只有一个元素的元组。要么删除逗号(将其留给 __iadd__ 方法将名称设置为 None)，要么在每个逗号后提供一个名称元素。