The comparison to Go's defer statement is interesting, though: ContextStack.register basically *is* the same as defer. While a nested with statement is a better option in Python, if we ignore that for the moment, you *could* write that simply copying example:

    with ContextStack() as stack:
        src = open(source)
        stack.register(src.close)
        dest = open(destination, 'w')
        stack.register(dest.close)
        copy(src, dest)

However, since ContextStack is just an ordinary context manager class, you have a lot of flexibility in what you do with it (particularly once I add the preserve() API to let you deliberately *skip* the cleanup steps by transferring them to a new ContextStack object)