1 files changed, 41 insertions, 0 deletions
diff --git a/netmodel/util/singleton.py b/netmodel/util/singleton.py
new file mode 100644
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+++ b/netmodel/util/singleton.py
@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+#
+# Copyright (c) 2017 Cisco and/or its affiliates.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+class Singleton(type):
+    """
+    Classes that inherit from Singleton can be instanciated only once 
+
+    See also
+    http://stackoverflow.com/questions/6760685/creating-a-singleton-in-python
+    """
+
+    def __init__(cls, name, bases, dic):
+        super(Singleton,cls).__init__(name,bases,dic)
+        cls.instance=None
+
+    def __call__(cls, *args, **kw):
+        if cls.instance is None:
+            cls.instance=super(Singleton,cls).__call__(*args,**kw)
+        return cls.instance
+
+    def _drop(cls):
+        "Drop the instance (for testing purposes)."
+        if cls.instance is not None:
+            del cls.instance
+            cls.instance = None
+