The constants defined in this class are used to get or set attributes (through Model.getAttr or Model.setAttr, for example). Please refer to the Attributes section to see a list of all attributes and their functions. You refer to an attribute using a GRB.Attr prefix (e.g., GRB.Attr.Obj). Note that these constants are simply strings, so wherever you might use this constant, you also have the option of using the string directly (e.g, 'obj' rather than GRB.Attr.Obj).