# Source code for taurus.core.util.singleton

    #!/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):  # 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

        def init(self, *p, **k):
            pass