Gurobi constraint object. Constraints are always associated with a particular model. You create a constraint object by adding a constraint to a model (using Model.addConstr), rather than by using a Constr constructor.

Constraint objects have a number of attributes. The full list can be found in the Attributes section of this document. Some constraint attributes can only be queried, while others can also be set. Recall that the Gurobi optimizer employs a lazy update approach, so changes to attributes don't take effect until the next call to Model.update, Model.optimize, or Model.write on the associated model.

We should point out a few things about constraint attributes. Consider the rhs attribute. Its value can be queried using constr.rhs. The Gurobi library ignores letter case in attribute names, so it can also be queried as constr.rhs. It can be set using a standard assignment statement (e.g., constr.rhs = 0). However, as mentioned earlier, attribute modification is done in a lazy fashion, so you won't see the effect of the change immediately. And some attributes can not be set (e.g., the Pi attribute), so attempts to assign new values to them will raise an exception.

You can also use Constr.getAttr/ Constr.setAttr to access attributes. The attribute name can be passed to these routines as a string, or you can use the constants defined in the GRB.Attr class (e.g., GRB.Attr.RHS).