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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 GetClientURNsForHostnames(hostnames, token=None):
 """Gets all client_ids for a given list of hostnames or FQDNS. Args: hostnames: A list of hostnames / FQDNs. token: An ACL token. Returns: A dict with a list of all known GRR client_ids for each hostname. """


  if data_store.RelationalDBEnabled():
    index = ClientIndex()
  else:
    index = CreateClientIndex(token=token)

  keywords = set()
  for hostname in hostnames:
    if hostname.startswith("host:"):
      keywords.add(hostname)
    else:
      keywords.add("host:%s" % hostname)
  results = index.ReadClientPostingLists(keywords)

  result = {}
  for keyword, hits in iteritems(results):
    result[keyword[len("host:"):]] = hits
  return result