human
Solve the following python programming problem given the following code:
def call_highest_priority(method_name) : 
    "A decorator for binary special methods to handle _op_priority.

    Binary special methods in Expr and its subclasses use a special attribute
    '_op_priority' to determine whose special method will be called to
    handle the operation. In general, the object having the highest value of
    '_op_priority' will handle the operation. Expr and subclasses that define
    custom binary special methods (__mul__, etc.) should decorate those
    methods with this decorator to add the priority logic.

    The ``method_name`` argument is the name of the method of the other class
    that will be called.  Use this decorator in the following manner::

        # Call other.__rmul__ if other._op_priority > self._op_priority
        @call_highest_priority('__rmul__')
        def __mul__(self, other):
            ...

        # Call other.__mul__ if other._op_priority > self._op_priority
        @call_highest_priority('__mul__')
        def __rmul__(self, other):
        ...
    " 
    def priority_decorator(func) : 
        @ wraps (func) 
        def binary_op_wrapper(self, other) : 
            if hasattr (other, '_op_priority') : 
                if (other._op_priority > self._op_priority) : 
                    try : 
                        f = getattr (other, method_name) 
except AttributeError : 
                        pass 
else : 
                        return f (self) 
return func (self, other) 
return binary_op_wrapper 
return <MASK> 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is Python code to determine whose special method will be called to
.
def priority_decorator(