Python Attribute Examples


Python Attribute Examples

Consider the case where you have a Gurobi model m. You can retrieve the number of variables in the model by querying the NumVars model attribute:

  print(m.numVars)
(Note that attribute capitalization doesn't matter in the Python interface, so you could also query m.NumVars or m.numvars).

If you've performed optimization on the model, the optimal objective value can be obtained by querying the ObjVal model attribute:

  print(m.objVal)

If you'd like to query the value that a variable takes in the computed solution, you can query the X attribute for the corresponding variable object:

  for v in m.getVars():
    print(v.x)
You can also query the value of X for multiple variables in a single getAttr call on the model m:
  print(m.getAttr(GRB.Attr.X, m.getVars()))

For each attribute query method, there's an analogous set routine. To set the upper bound of a variable, for example:

  v = m.getVars()[0]
  v.ub = 0
(In this example, we've set the upper bound for the first variable in the model to 0).