different beween self.null and none in Red black tree implementation-CodePudding

I don't understand a piece of code from the implementation of the black red tree please say what self.null here means and what's the difference with none? Why we have some places none, but some places self.null thanks. If I used these two instead of each other, that means I'd put none instead of self.null, then what would have happened?

class Node():
    def __init__(self,val):
        self.val = val                                   # Value of Node
        self.parent = None                               # Parent of Node
        self.left = None                                 # Left Child of Node
        self.right = None                                # Right Child of Node
        self.color = 1                                   # Red Node as new node is always inserted as Red Node

# Define R-B Tree
class RBTree():
    def __init__(self):
        self.NULL = Node ( 0 )
        self.NULL.color = 0
        self.NULL.left = None
        self.NULL.right = None
        self.root = self.NULL


    # Insert New Node
    def insertNode(self, key):
        node = Node(key)
        node.parent = None
        node.val = key
        node.left = self.NULL
        node.right = self.NULL
        node.color = 1                                   # Set root colour as Red

        y = None
        x = self.root

        while x != self.NULL :                           # Find position for new node
            y = x
            if node.val < x.val :
                x = x.left
            else :
                x = x.right

I tried to understand the difference between self.null and none, but I couldn't. especially in this line x! self.null

CodePudding user response：

Self.NULL is called a "sentinel node". It's an actual Node object that is used in place of a None or null value at all the places in the tree where nodes are missing.

This is commonly used in red-black trees to simplify the code. The code is simpler, because you can check the color of a sentinel node (nulls are black) without testing first to see if the node exists. This removes a lot if if node == None checks that would otherwise be required.