Append a variable to a list

Answered

Sanaa MARZOUG

August 29, 2022 20:22

• 
• 

hello,

I am trying to append a gurobi varible to a list with this code:

Prod_values = {}
obj_vars = []
Plants = range(7)
for l in range(7):
    for p in Demand:
        for d in Horizon:
            Prod_values = model.addVars(Plants,Demand,Horizon,lb = 0, vtype =GRB.INTEGER, name ='Prod_engrais')
            obj_vars.append(Prod_values[(l,p,d)])

but when i print obj_vars, it doesn't return the same values as Prod_values. Could you provide me with some help. 

Thank you for reading this post and helping me out!

0

• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  November 16, 2025 23:29

  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 try Gurobot, our chatbot interface offering instant, expert-level support.
• 

  Jaromił Najman

  • Gurobi Staff

  August 30, 2022 12:15

  Hi Sanaa,

  Please note that your example is not reproducible, because values for Demand and Horizon are missing.

  Moreover, you are adding Plants x Demand x Horizon variable in each loop iteration by using the addVars method. If you want to assign a value to a certain dictionary field, you have to access it via \(\texttt{Prod_values[l,p,d] = ...}\)

  What you are probably looking for is something like

  import gurobipy as gp
  from gurobipy import GRB
  
  model = gp.Model()
  
  Prod_values = {}
  obj_vars = []
  Plants = range(4)
  Demand = range(3)
  Horizon = range(2)
  for l in Plants:
      for p in Demand:
          for d in Horizon:
              Prod_values[l,p,d] = model.addVar(lb = 0, vtype =GRB.INTEGER, name ='Prod_engrais[%d,%d,%d]'%(l,p,d))
              obj_vars.append(Prod_values[(l,p,d)])
  model.update()
  print(Prod_values)
  print(obj_vars)

  Best regards, 
  Jaromił

  0

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