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# gurobipy.SOS

class SOS

  Gurobi SOS constraint object. SOS constraints are always associated with a particular model. You create an SOS object by adding an SOS constraint to a model (using `Model.addSOS`), rather than by using an SOS constructor. Similarly, SOS constraints are removed using the `Model.remove` method.

  An SOS constraint can be of type 1 or 2 (`GRB.SOS_TYPE1` or `GRB.SOS_TYPE2`). A type 1 SOS constraint is a set of variables where at most one variable in the set may take a value other than zero. A type 2 SOS constraint is an ordered set of variables where at most two variables in the set may take non-zero values. If two take non-zero values, they must be contiguous in the ordered set.

  SOS constraint objects have a number of attributes, e.g., IISSOS, which can be queried with the `SOS.getAttr` method.

  The full list of attributes can be found in the Attributes section of this document. Examples of how to query and set attributes can also be found in this section.

  getAttr(attrname)

    Query the value of an SOS attribute.

    Raises an `AttributeError` if the requested attribute doesn’t exist or can’t be queried. Raises a `GurobiError` if there is a problem with the `SOS` object (e.g., it was removed from the model).

    Parameters:

      attrname – The attribute being queried.

    Returns:

      The current value of the requested attribute.

    Example:

          print(sos.getAttr(GRB.Attr.IISSOS))

  property index

    This property returns the current index, or order, of the SOS constraint in the underlying model.

    Note that the index of an SOS constraint may change after subsequent model modifications.

    Returns:

      -2: removed, -1: not in model, otherwise: index of the SOS constraint in the model

  setAttr(attrname, newvalue)

    Set the value of an SOS attribute. Note that, due to our lazy update approach, the change won’t actually take effect until you update the model (using `Model.update`), optimize the model (using `Model.optimize`), or write the model to disk (using `Model.write`).

    Raises an `AttributeError` if the specified attribute doesn’t exist or can’t be set. Raises a `GurobiError` if there is a problem with the `SOS` object (e.g., it was removed from the model).

    Parameters:

      - attrname – The attribute being modified.

      - newvalue – The desired new value of the attribute.

    Example:

          sos.setAttr(GRB.Attr.IISSOSForce, 1)
          var.setAttr("IISSOSForce", 0.0)

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