Initial import from Docker volume

tools/singleton.py

@@ -0,0 +1,16 @@
+# This file is part of Tryton.  The COPYRIGHT file at the top level of
+# this repository contains the full copyright notices and license terms.
+
+
+class Singleton(type):
+    '''
+    Metaclass for singleton pattern
+    '''
+    def __init__(cls, name, bases, dict):
+        super(Singleton, cls).__init__(name, bases, dict)
+        cls.instance = None
+
+    def __call__(cls, *args, **kwargs):
+        if cls.instance is None:
+            cls.instance = super(Singleton, cls).__call__(*args, **kwargs)
+        return cls.instance