Chore(signgletone): Add new concept of implement

Author: rezamobaraki

src/singleton2.py

@@ -3,7 +3,6 @@
         Singleton
 """
 
-
 class Singleton(type):
     _instance = None
 
@@ -13,6 +12,25 @@ def __call__(cls, *args, **kwargs):
         return cls._instance
 
 
+class Singleton(type):
+    """
+    Singleton metaclass
+    Based on Python Cookbook 3rd Edition Recipe 9.13
+    Only one instance of a class can exist. Does not work with __slots__
+    """
+
+    def __init__(self, *args, **kw):
+        super(Singleton, self).__init__(*args, **kw)
+        self.__instance = None
+
+    def __call__(self, *args, **kw):
+        if self.__instance is None:
+            self.__instance = super(Singleton, self).__call__(*args, **kw)
+        return self.__instance
+
+   
+
+   
 class DB(metaclass=Singleton):
     pass