instance.py

"""
The shared instance implementation by using
captured lexical variable bindings.
"""

class A(object):

    @staticmethod
    def shared():
        """
        Returns the shared instance of A.

        >>> A.shared()  #doctest: +ELLIPSIS
        <__main__.A ...>
        >>> A.shared() is A.shared()
        True
        """
        instance = A()
        A.shared = staticmethod(lambda: instance)
        return instance


if __name__ == "__main__":
    import doctest
    doctest.testmod()