Use method initialize to pass settings

settings.py

@@ -1,10 +1,9 @@
 import logging
 import os.path
 import uuid
-import paramiko
 
-from tornado.options import define, options
-from policy import get_host_keys, get_policy_class
+from tornado.options import define
+from policy import get_host_keys, get_policy_class, check_policy_setting
 
 
 define('address', default='127.0.0.1', help='listen address')
@@ -12,32 +11,47 @@ define('port', default=8888, help='listen port', type=int)
 define('debug', default=False, help='debug mode', type=bool)
 define('policy', default='warning',
        help='missing host key policy, reject|autoadd|warning')
+define('hostFile', default='', help='User-defined host keys file')
+define('sysHostFile', default='', help='System-wide host keys File')
 
 
-def get_application_settings():
-    base_dir = os.path.dirname(__file__)
-    filename = os.path.join(base_dir, 'known_hosts')
-    host_keys = get_host_keys(filename)
-    system_host_keys = get_host_keys(os.path.expanduser('~/.ssh/known_hosts'))
-    policy_class = get_policy_class(options.policy)
-    logging.info(policy_class.__name__)
+base_dir = os.path.dirname(__file__)
 
-    if policy_class is paramiko.client.AutoAddPolicy:
-        host_keys.save(filename)  # for permission test
-    elif policy_class is paramiko.client.RejectPolicy:
-        if not host_keys and not system_host_keys:
-            raise ValueError('Empty known_hosts with reject policy?')
 
+def get_app_settings(options):
     settings = dict(
         template_path=os.path.join(base_dir, 'templates'),
         static_path=os.path.join(base_dir, 'static'),
         cookie_secret=uuid.uuid4().hex,
         xsrf_cookies=True,
-        host_keys=host_keys,
-        host_keys_filename=filename,
-        system_host_keys=system_host_keys,
-        policy=policy_class(),
         debug=options.debug
     )
-
     return settings
+
+
+def get_host_keys_settings(options):
+    if not options.hostFile:
+        host_keys_filename = os.path.join(base_dir, 'known_hosts')
+    else:
+        host_keys_filename = options.hostFile
+    host_keys = get_host_keys(host_keys_filename)
+
+    if not options.sysHostFile:
+        filename = os.path.expanduser('~/.ssh/known_hosts')
+    else:
+        filename = options.sysHostFile
+    system_host_keys = get_host_keys(filename)
+
+    settings = dict(
+        host_keys=host_keys,
+        system_host_keys=system_host_keys,
+        host_keys_filename=host_keys_filename
+    )
+    return settings
+
+
+def get_policy_setting(options, host_keys_settings):
+    policy_class = get_policy_class(options.policy)
+    logging.info(policy_class.__name__)
+    check_policy_setting(policy_class, host_keys_settings)
+    return policy_class()