Return the code for the role,  measure, dimension or error

def role(self):
        '''Return the code for the role,  measure, dimension or error'''
        from ambry.valuetype.core import ROLE

        if not self.valuetype_class:
            return ''

        role = self.valuetype_class.role
        if role == ROLE.UNKNOWN:
            vt_code = self.valuetype_class.vt_code

            if len(vt_code) == 1 or vt_code[1] == '/':
                return vt_code[0]
            else:
                return ''

        return role