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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def close(self):
        '''Close all the connections and clean up.

        This instance will not be usable after calling this method.
        '''
        for key, pool in tuple(self._host_pools.items()):
            pool.close()

            del self._host_pools[key]
            del self._host_pool_waiters[key]

        self._closed = True