code: def GetUnreachableInstances(instances, ssh_key):
    
    hostnames = [i.private_ip for i in instances]
    ssh_status = AreHostsReachable(hostnames, ssh_key)
    assert(len(hostnames) == len(ssh_status))
    nonresponsive_instances = [instance for (instance, ssh_ok) in
                               zip(instances, ssh_status) if not ssh_ok]
    return nonresponsive_instances
docs: Returns list of instances unreachable via ssh.