How to use the memoization.memoization_py2._CacheNode.root function in memoization

last_node.destroy()

            if first_freq_node.cache_head.next == first_freq_node.cache_head:
                # Getting here means that we just deleted the only data node in the cache list
                # under the first frequency list
                # Note: there is still an empty sentinel node
                # We then need to destroy the sentinel node and its parent frequency node too
                first_freq_node.cache_head.destroy()
                first_freq_node.destroy()
                first_freq_node = root.next  # update

            # Delete from cache
            del cache[old_key]

            # Prepare a new frequency node, a cache root node and a cache data node
            empty_cache_root = _CacheNode.root()
            freq_node = _FreqNode(root, first_freq_node, 1, empty_cache_root)
            cache_node = _CacheNode(empty_cache_root, empty_cache_root, freq_node, key, value)
            empty_cache_root.parent = freq_node

            # Modify references
            root.next.prev = root.next = freq_node
            empty_cache_root.prev = empty_cache_root.next = cache_node

        else:
            # We can find the last element in the cache list under the first frequency list
            # Moving it to the head and replace the stored data with a new key and a new value
            # This is more efficient

            # Find the target
            cache_head = first_freq_node.cache_head
            manipulated_node = cache_head.prev

# use another name so it can be accessed later
            cache_node = manipulated_node

            # Delete from cache
            del cache[old_key]
    else:
        # The cache is not full

        if first_freq_node.frequency != 1:
            # The first element in frequency list has its frequency other than 1 (> 1)
            # Creating a new node in frequency list with 1 as its frequency required
            # We also need to create a new cache list and attach it to this new node

            # Create a cache root and a frequency node
            cache_root = _CacheNode.root()
            freq_node = _FreqNode(root, first_freq_node, 1, cache_root)
            cache_root.parent = freq_node

            # Create another cache node to store data
            cache_node = _CacheNode(cache_root, cache_root, freq_node, key, value)

            # Modify references
            cache_root.prev = cache_root.next = cache_node
            first_freq_node.prev = root.next = freq_node  # note: DO NOT swap "=", because first_freq_node == root.next

        else:
            # We create a new cache node in the cache list
            # under the frequency node with frequency 1

            # Create a cache node and store data in it
            cache_head = first_freq_node.cache_head

if key in cache:
        cache_node = cache[key]
    else:
        # Key does not exist
        # Access failed
        return sentinel
    freq_node = cache_node.parent
    target_frequency = freq_node.frequency + 1
    if freq_node.next.frequency != target_frequency:
        # The next node on the frequency list has a frequency value different from
        # (the frequency of the current node) + 1, which means we need to construct
        # a new frequency node and an empty cache root node
        # Then we move the current node to the newly created cache list

        # Create a cache root and a frequency root
        cache_root = _CacheNode.root()
        new_freq_node = _FreqNode(freq_node, freq_node.next, target_frequency, cache_root)
        cache_root.parent = new_freq_node

        # Modify references
        cache_node.prev.next = cache_node.next
        cache_node.next.prev = cache_node.prev
        cache_node.prev = cache_node.next = cache_root
        cache_root.prev = cache_root.next = cache_node
        new_freq_node.next.prev = new_freq_node.prev.next = new_freq_node
        cache_node.parent = cache_root.parent

    else:
        # We can move the cache node to the cache list of the next node on the frequency list

        # Find the head element of the next cache list
        next_cache_head = freq_node.next.cache_head