getAttr ( attrname )
Query the value of a constraint 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
Constr object (e.g., it was removed from the model).
attrname: The attribute being queried.
The current value of the requested attribute.