def traverse_check_before(node, depth, cache):
    cache[node] = None

    print('__'*depth + node.name)
    for ref in node.refs:
        # we are about to recurse, first check if the node we want
        # to recurse on is in the cache
        if ref in cache:
            print('Already in cache: %s' % ref.name)
            continue
        # recurse if we reach this point
        traverse_cached(ref, depth+1, cache)


def traverse_check_after(node, depth, cache):
    # we have just recursed, return if this node is already in
    # the cache
    if node in cache:
        print('Already in cache: %s' % node.name)
        return
    cache[node] = None

    print('__'*depth + node.name)
    for ref in node.refs:
        # recurse without exception
        traverse_cached(ref, depth+1, cache)