def add_class(self, ioclass):
current_ioclasses = self.ioclasses<EOL>if ioclass.name in current_ioclasses.name:<EOL><INDENT>return<EOL><DEDENT>current_ioclasses.append(ioclass)<EOL>self.modify(new_ioclasses=current_ioclasses)<EOL>
Add one VNXIOClass instance to policy.

        .. note: due to the limitation of VNX, need to stop the policy first.