TypeError:object of type 'gurobipy.gurobipy.LinExpr' has no len()

Answered

FEI XUE

June 11, 2021 08:40

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I need to add some constraints into my model.

The code and formula are as follows.

for i in range(1, n - 1):
    for k in range(3, n):
        BASE.addConstr(
            ntk3[i, k]
            == min_(
                quicksum(htk[t, k] for t in range(i, i + 3)),
                3 - quicksum(htk[t, k] for t in range(i, i + 3)),
            )
        )

Where h_ik is the 0-1 variable.

Gurobi always appears this TypeError:object of type 'gurobipy.gurobipy.LinExpr' has no len()

Looking forward to your reply.

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 02:53 Edited

  This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum. Or why not try our AI Gurobot?.
• 

  Eli Towle

  • Gurobi Staff

  June 11, 2021 17:58

  The min_() helper function takes a list of Var objects and/or constants as arguments. Both of the arguments in your example are LinExpr objects.

  To resolve the issue, add auxiliary variables to the model and set them equal to the linear expressions passed as arguments to the min_() function. Then, pass the corresponding Var objects as arguments to min_() instead.

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  FEI XUE

  June 12, 2021 08:03

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  Mr. Towle

  thank you for your reply. I will try again.

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