getAttr ( attrname )
Query the value of an SOS attribute. The full list of available attributes can be found in the Attributes section.
AttributeError if the requested attribute doesn't
exist or can't be queried.
GurobiError if there is a problem with the
SOS object (e.g., it was removed from the model).
attrname: The attribute being queried.
The current value of the requested attribute.