def instance(obj):
    """
    Return the instance the proxy is wrapping.

    Usage:

    >>> class Example(object):
    ...     pass
    >>> class Proxy(object):
    ...     pass
    >>> Proxy = wrap_with(Example)
    >>> example = Example()
    >>> proxy_obj = Proxy(example)
    >>> instance(proxy_obj) is example
    True
    """
    return obj.__instance__
