<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def get_preferred(self, addr_1, addr_2):
        '''Return the preferred address.'''
        if addr_1 > addr_2:
            addr_1, addr_2 = addr_2, addr_1

        return self._cache.get((addr_1, addr_2))