docs: def get_user_list(host_name, client_name, client_pass):
      """
      Pulls the list of users in a client.
  
      Inputs: - host_name: A string containing the address of the machine where the PServer instance is hosted.
              - client_name: The PServer client name.
              - client_pass: The PServer client's password.
  
      Output: - user_id_list: A python list of user ids.
      """
      # Construct request.
      request = construct_request(model_type="pers",
                                  client_name=client_name,
                                  client_pass=client_pass,
                                  command="getusrs",
                                  values="whr=*")
  
      # Make request.
      request_result = send_request(host_name, request)
  
      # Extract a python list from xml object.
      user_id_list = list()
      append_user_id = user_id_list.append
  
      if request_result is not None:
          user_list_xml = request_result.text
          tree = etree.parse(StringIO(user_list_xml))
          root = tree.getroot()
  
          xml_rows = root.findall("./result/row/usr")
          for xml_row in xml_rows:
              append_user_id(xml_row.text)
  
      return user_id_list