Software Público Brasileiro

#!/usr/bin/python

#  singleton - python class that implements singleton design pattern.
#
#  Copyright (C) 2010  Tassia Camoes <tassia@gmail.com>
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation, either version 3 of the License, or
#  (at your option) any later version.
#
#  This program 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 General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program.  If not, see <http://www.gnu.org/licenses/>.
class Singleton(object):
    """
    Base class for inheritance of only-one-instance classes.
    Singleton design pattern.
    """
    def __new__(cls, *args, **kwargs):
        """
        Creates a new instance of the class only if none already exists.
        """
        if '_inst' not in vars(cls):
            cls._inst = object.__new__(cls)
        return cls._inst