Python – Property error : ‘gurobipy. LinExpr’ object has no attribute ‘__colno__’

I’m trying to model a MILP problem using Python and Gurobi Solver. I have the latest version of the Gurobi solver. My problem started after I added a constraint using the new function of gurobi m.addGenConstrAbs, which added the abs value of the function as a constraint. Here is my code, which creates a gurobi feedback:

AttributeError: ‘gurobipy. The LinExpr’ object does not have the attribute ‘__colno__’.

My code that generated this feedback is:

for t in range(0,Period): 
 m.addGenConstrAbs(PEN[t], EG [t]+STG[t]-XXX, "PEN Constraint") 

where EG[t],

STD[t], and XXX are decision variables.

I don’t understand why Gurobi or Python return this error. What do you think the problem is? Thank you.

Model.addGenConstrAbs() must be a variable (Var), not a linear expression (LinExpr). Try this :

for t in range(0,Period):
    z = m.addVar(lb=-GRB. INFINITY)
    m.addConstr(z == EG[t]+STG[t]-XXX)
    m.addGenConstrAbs(PEN[t], z, "PEN Constraint")