able of the function.  The problem with that is
    that you can only associate one piece of data with every C++
    function, and we have no way of compiling a new C++ function
    on-the-fly for every Python function you decide to pass
    to <code>foo</code>.  In other words, this could work if the C++
    function is always going to invoke the <em>same</em> Python
    function, but you probably don't want that.

    <p>If you have the luxury of changing the C++ code you're
    wrapping, pass it an <code