#!/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"
[docs]
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): # noqa: E721
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
[docs]
def init(self, *p, **k):
pass