environment/lib/python2.7/site-packages/IPython/config/configurable.py
def instance(cls, *args, **kwargs):
        """Returns a global instance of this class.

        This method create a new instance if none have previously been created
        and returns a previously created instance is one already exists.

        The arguments and keyword arguments passed to this method are passed
        on to the :meth:`__init__` method of the class upon instantiation.

        Examples
        --------

        Create a singleton class using instance, and retrieve it::

            >>> from IPython.config.configurable import SingletonConfigurable
            >>> class Foo(SingletonConfigurable): pass
            >>> foo = Foo.instance()
            >>> foo == Foo.instance()
            True

        Create a subclass that is retrived using the base class instance::

            >>> class Bar(SingletonConfigurable): pass
            >>> class Bam(Bar): pass
            >>> bam = Bam.instance()
            >>> bam == Bar.instance()
            True
        """
        # Create and save the instance
        if cls._instance is None:
            inst = cls(*args, **kwargs)
            # Now make sure that the instance will also be returned by
            # parent classes' _instance attribute.
            for subclass in cls._walk_mro():
                subclass._instance = inst

        if isinstance(cls._instance, cls):
            return cls._instance
        else:
            raise MultipleInstanceError(
                'Multiple incompatible subclass instances of '
                '%s are being created.' % cls.__name__
            )
def instance(cls, *args, **kwargs):
        """Returns a global instance of this class.

        This method create a new instance if none have previously been created
        and returns a previously created instance is one already exists.

        The arguments and keyword arguments passed to this method are passed
        on to the :meth:`__init__` method of the class upon instantiation.

        Examples
        --------

        Create a singleton class using instance, and retrieve it::

            >>> from IPython.config.configurable import SingletonConfigurable
            >>> class Foo(SingletonConfigurable): pass
            >>> foo = Foo.instance()
            >>> foo == Foo.instance()
            True

        Create a subclass that is retrived using the base class instance::

            >>> class Bar(SingletonConfigurable): pass
            >>> class Bam(Bar): pass
            >>> bam = Bam.instance()
            >>> bam == Bar.instance()
            True
        """
        # Create and save the instance
        if cls._instance is None:
            inst = cls(*args, **kwargs)
            # Now make sure that the instance will also be returned by
            # parent classes' _instance attribute.
            for subclass in cls._walk_mro():
                subclass._instance = inst

        if isinstance(cls._instance, cls):
            return cls._instance
        else:
            raise MultipleInstanceError(
                'Multiple incompatible subclass instances of '
                '%s are being created.' % cls.__name__
            )
Returns a global instance of this class.

        This method create a new instance if none have previously been created
        and returns a previously created instance is one already exists.

        The arguments and keyword arguments passed to this method are passed
        on to the :meth:`__init__` method of the class upon instantiation.

        Examples
        --------

        Create a singleton class using instance, and retrieve it::

            >>> from IPython.config.configurable import SingletonConfigurable
            >>> class Foo(SingletonConfigurable): pass
            >>> foo = Foo.instance()
            >>> foo == Foo.instance()
            True

        Create a subclass that is retrived using the base class instance::

            >>> class Bar(SingletonConfigurable): pass
            >>> class Bam(Bar): pass
            >>> bam = Bam.instance()
            >>> bam == Bar.instance()
            True