osm_mon/plugins/OpenStack/singleton.py

   1 # Copyright 2017 Intel Research and Development Ireland Limited
   2 # *************************************************************
   3
   4 # This file is part of OSM Monitoring module
   5 # All Rights Reserved to Intel Corporation
   6
   7 # Licensed under the Apache License, Version 2.0 (the "License"); you may
   8 # not use this file except in compliance with the License. You may obtain
   9 # a copy of the License at
  10
  11 #         http://www.apache.org/licenses/LICENSE-2.0
  12
  13 # Unless required by applicable law or agreed to in writing, software
  14 # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  15 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  16 # License for the specific language governing permissions and limitations
  17 # under the License.
  18
  19 # For those usages not covered by the Apache License, Version 2.0 please
  20 # contact: helena.mcgough@intel.com or adrian.hoban@intel.com
  21 ##
  22 """Simple singleton class."""
  23
  24 from __future__ import unicode_literals
  25
  26 __author__ = "Helena McGough"
  27
  28
  29 class Singleton(object):
  30     """Simple singleton class."""
  31
  32     def __init__(self, decorated):
  33         """Initialize singleton instance."""
  34         self._decorated = decorated
  35
  36     def instance(self):
  37         """Return singleton instance."""
  38         try:
  39             return self._instance
  40         except AttributeError:
  41             self._instance = self._decorated()
  42             return self._instance