Fix YAQL engine initialization

* When Mistral is launched via launch.py script then YAQL engine class
  initialization logic doesn't use the right properties from the config
  file. This is because this initialization is caused by the chain of
  imports taking its start in launch.py, and this happens before
  the config file is parsed in the main() function of launch.py.
  Using lazy initialization of YAQL engine class (YAQL_ENGINE in
  yaql_expression.py module) solves this issue because now Mistral
  doesn't initialize it immediately before parsing the config and
  waits for the first usage of it.
* Minor style changes per Mistral coding guidelines.

Change-Id: If3367493803b57ef8bc281b1f64f2a223ac86f85
Closes-Bug: #1864785

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
 
 

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: