osm_policy_module/core/singleton.py

   1 # -*- coding: utf-8 -*-
   2
   3 # Copyright 2018 Whitestack, LLC
   4 # *************************************************************
   5
   6 # This file is part of OSM Monitoring module
   7 # All Rights Reserved to Whitestack, LLC
   8
   9 # Licensed under the Apache License, Version 2.0 (the "License"); you may
  10 # not use this file except in compliance with the License. You may obtain
  11 # a copy of the License at
  12
  13 #         http://www.apache.org/licenses/LICENSE-2.0
  14
  15 # Unless required by applicable law or agreed to in writing, software
  16 # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  17 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  18 # License for the specific language governing permissions and limitations
  19 # under the License.
  20
  21 # For those usages not covered by the Apache License, Version 2.0 please
  22 # contact: bdiaz@whitestack.com or glavado@whitestack.com
  23 ##
  24 """Simple singleton class."""
  25
  26 from __future__ import unicode_literals
  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