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#!/usr/bin/env python
#############################################################################
##
## This file is part of Taurus
##
## http://taurus-scada.org
##
## Copyright 2011 CELLS / ALBA Synchrotron, Bellaterra, Spain
##
## Taurus is free software: you can redistribute it and/or modify
## it under the terms of the GNU Lesser General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## Taurus is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU Lesser General Public License for more details.
##
## You should have received a copy of the GNU Lesser General Public License
## along with Taurus. If not, see <http://www.gnu.org/licenses/>.
##
#############################################################################
"""This module contains a class which can be used as a super class for all
classes that need to implement the Singleton design pattern."""
__all__ = ["Singleton"]
__docformat__ = "restructuredtext"
class Singleton(object):
""" This class allows Singleton objects
The __new__ method is overriden to force Singleton behaviour.
The Singleton is created for the lowest subclass.
Usage::
from taurus.core.util.singleton import Singleton
class MyManager(Singleton):
def init(self, *args, **kwargs):
print "Singleton initialization"
command line::
>>> manager1 = MyManager()
Singleton initialization
>>> manager2 = MyManager()
>>> print(manager1,manager2)
<__main__.MyManager object at 0x9c2a0ec>
<__main__.MyManager object at 0x9c2a0ec>
Notice that the two instances of manager point to the same object even
though you *tried* to construct two instances of MyManager.
.. warning::
although __new__ is overriden __init__ is still being called for
each instance=Singleton()
"""
## Singleton object
_the_instance = None
def __new__(cls, *p, **k):
#srubio: added type checking
if cls != type(cls._the_instance):
cls._the_instance = object.__new__(cls)
#srubio: added init_single check
if 'init_single' in cls.__dict__:
cls._the_instance.init_single(*p,**k)
else: cls._the_instance.init(*p,**k)
return cls._the_instance
def init(self, *p,**k):
pass
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