AttributeError: 'dict' object has no attribute 'prod'

Answered

Leonardo Miranda

• July 03, 2023 14:57

When running the diet.py example, the line m.setObjective(buy.prod(cost), GRB.MINIMIZE) is displaying the following error: AttributeError: 'dict' object has no attribute 'prod'. To create the "buy" object, I used the line  "for f in foods: buy[f] = m.addVar(name=f)". I noticed that "buy" is a dictionary type and not a tuple dictionary. Does anyone know why?

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• Python

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• 

  Eli Towle

  Gurobi Staff

  • July 03, 2023 23:57

  In the original version of the example, the \(\texttt{buy}\) variables are added using Model.addVars() method. This method returns a tupledict object:

  buy = m.addVars(foods, name="buy")

  In the alternative version, \(\texttt{buy}\) is constructed as a standard Python \(\texttt{dict}\). The values of this dictionary are set to the individual Var objects returned by Model.addVar():

  buy = {}
  for f in foods:
      buy[f] = m.addVar(name=f)

  You can convert \(\text{buy}\) to a tupledict using the tupledict() constructor:

  buy = gp.tupledict(buy)

  This should allow you to use the tupledict.prod() and tupledict.sum() methods.

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