human
Solve the following python programming problem given the following code:
@ classmethod 
def register(cls, policy_type) : 
    '
        Decorator for Storage Policy implementations to register
        their StoragePolicy class.  This will also set the policy_type
        attribute on the registered implementation.
        ' 
    def register_wrapper(policy_cls) : 
        if (policy_type in cls.policy_type_to_policy_cls) : 
            raise PolicyError (('%r is already registered for the policy_type %r' % (cls.policy_type_to_policy_cls [policy_type], policy_type))) 
cls.policy_type_to_policy_cls [policy_type] = policy_cls 
        policy_cls.policy_type = policy_type 
        return policy_cls 
return <MASK> 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def register_wrapper(