<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def GetUnreachableHosts(hostnames, ssh_key):
 """ Returns list of hosts unreachable via ssh. """

  ssh_status = AreHostsReachable(hostnames, ssh_key)
  assert(len(hostnames) == len(ssh_status))
  nonresponsive_hostnames = [host for (host, ssh_ok) in
                             zip(hostnames, ssh_status) if not ssh_ok]
  return nonresponsive_hostnames