[Mod] 改变Singleton的使用说明

vnpy/trader/engine.py

@@ -197,13 +197,11 @@ class BaseEngine(ABC):
         pass
 
 
-class LogEngine(BaseEngine):
+class LogEngine(BaseEngine, metaclass=Singleton):
     """
     Processes log event and output with logging module.
     """
 
-    __metaclass__ = Singleton
-
     def __init__(self, main_engine: MainEngine, event_engine: EventEngine):
         """"""
         super(LogEngine, self).__init__(main_engine, event_engine, "log")

vnpy/trader/utility.py

@@ -16,8 +16,9 @@ class Singleton(type):
     """
     Singleton metaclass,
 
-    class A:
-        __metaclass__ = Singleton
+    usage:
+    class A(metaclass=Singleton):
+        ...
     """
     _instances = {}