human
Solve the following python programming problem given the following code:
@ staticmethod 
def register_header_type(type_) : 
    def _register_header_type(cls) : 
        ipv6._IPV6_EXT_HEADER_TYPE [type_] = cls 
        return cls 
return <MASK> 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def _register_header_type(