diff --git a/mistral/cmd/launch.py b/mistral/cmd/launch.py
index 313452cc6..ebff6d218 100644
--- a/mistral/cmd/launch.py
+++ b/mistral/cmd/launch.py
@@ -32,9 +32,14 @@ import os
 
 # If ../mistral/__init__.py exists, add ../ to Python search path, so that
 # it will override what happens to be installed in /usr/(local/)lib/python...
-POSSIBLE_TOPDIR = os.path.normpath(os.path.join(os.path.abspath(sys.argv[0]),
-                                   os.pardir,
-                                   os.pardir))
+POSSIBLE_TOPDIR = os.path.normpath(
+    os.path.join(
+        os.path.abspath(sys.argv[0]),
+        os.pardir,
+        os.pardir
+    )
+)
+
 if os.path.exists(os.path.join(POSSIBLE_TOPDIR, 'mistral', '__init__.py')):
     sys.path.insert(0, POSSIBLE_TOPDIR)
 
@@ -177,7 +182,9 @@ def get_properly_ordered_parameters():
             else:
                 conf_file_value = args[args.index(arg) + 1]
                 args.remove(conf_file_value)
+
             args.remove(arg)
+
             args.insert(0, "--config-file")
             args.insert(1, conf_file_value)
 
@@ -188,9 +195,11 @@ def override_keystone_options():
     # TODO(wxy): This function is used for keeping backward compatibility.
     # Remove it in Stein.
     auth_opts = CONF['keystone_authtoken']
+
     for opt, value in auth_opts.items():
         if opt in CONF['keystone']:
             default_value = auth_opts._group._opts[opt]['opt'].default
+
             if default_value != value != CONF['keystone'][opt]:
                 LOG.warning("The config option '%s' in section "
                             "[keystone_authtoken] has the same copy in "
@@ -202,10 +211,13 @@ def override_keystone_options():
 def main():
     try:
         CONF.register_cli_opts(config.CLI_OPTS)
+
         config.parse_args(get_properly_ordered_parameters())
+
         print_server_info()
 
         logging.setup(CONF, 'Mistral')
+
         override_keystone_options()
 
         # Please refer to the oslo.messaging documentation for transport
@@ -246,6 +258,7 @@ def main():
 def reset_server_managers():
     global SERVER_THREAD_MANAGER
     global SERVER_PROCESS_MANAGER
+
     SERVER_THREAD_MANAGER = None
     SERVER_PROCESS_MANAGER = None
 
@@ -253,12 +266,14 @@ def reset_server_managers():
 # Helper method used in unit tests to access the service launcher.
 def get_server_thread_manager():
     global SERVER_THREAD_MANAGER
+
     return SERVER_THREAD_MANAGER
 
 
 # Helper method used in unit tests to access the process launcher.
 def get_server_process_manager():
     global SERVER_PROCESS_MANAGER
+
     return SERVER_PROCESS_MANAGER
 
 
diff --git a/mistral/expressions/yaql_expression.py b/mistral/expressions/yaql_expression.py
index 2a8f75302..36ac19a64 100644
--- a/mistral/expressions/yaql_expression.py
+++ b/mistral/expressions/yaql_expression.py
@@ -34,6 +34,10 @@ LOG = logging.getLogger(__name__)
 
 _YAQL_CONF = cfg.CONF.yaql
 
+INLINE_YAQL_REGEXP = '<%.*?%>'
+
+YAQL_ENGINE = None
+
 
 def get_yaql_engine_options():
     return {
@@ -54,24 +58,30 @@ def create_yaql_engine_class(keyword_operator, allow_delegates,
     ).create(options=engine_options)
 
 
-YAQL_ENGINE = create_yaql_engine_class(
-    _YAQL_CONF.keyword_operator,
-    _YAQL_CONF.allow_delegates,
-    get_yaql_engine_options()
-)
+def get_yaql_engine_class():
+    global YAQL_ENGINE
 
-LOG.info(
-    "YAQL engine has been initialized with the options: \n%s",
-    utils.merge_dicts(
-        get_yaql_engine_options(),
-        {
-            "keyword_operator": _YAQL_CONF.keyword_operator,
-            "allow_delegates": _YAQL_CONF.allow_delegates
-        }
+    if YAQL_ENGINE is not None:
+        return YAQL_ENGINE
+
+    YAQL_ENGINE = create_yaql_engine_class(
+        _YAQL_CONF.keyword_operator,
+        _YAQL_CONF.allow_delegates,
+        get_yaql_engine_options()
     )
-)
 
-INLINE_YAQL_REGEXP = '<%.*?%>'
+    LOG.info(
+        "YAQL engine has been initialized with the options: \n%s",
+        utils.merge_dicts(
+            get_yaql_engine_options(),
+            {
+                "keyword_operator": _YAQL_CONF.keyword_operator,
+                "allow_delegates": _YAQL_CONF.allow_delegates
+            }
+        )
+    )
+
+    return YAQL_ENGINE
 
 
 def _sanitize_yaql_result(result):
@@ -91,7 +101,7 @@ class YAQLEvaluator(Evaluator):
     @classmethod
     def validate(cls, expression):
         try:
-            YAQL_ENGINE(expression)
+            get_yaql_engine_class()(expression)
         except (yaql_exc.YaqlException, KeyError, ValueError, TypeError) as e:
             raise exc.YaqlGrammarException(getattr(e, 'message', e))
 
@@ -100,7 +110,7 @@ class YAQLEvaluator(Evaluator):
         expression = expression.strip() if expression else expression
 
         try:
-            result = YAQL_ENGINE(expression).evaluate(
+            result = get_yaql_engine_class()(expression).evaluate(
                 context=expression_utils.get_yaql_context(data_context)
             )
         except Exception as e: