在二叉树python结构中创建根节点

Question

class Tree:
    class Node:
        def __init__(self, left=None, right=None, parent=None, element=None):
            self.left = left
            self.right = right
            self.parent = parent
            self.element = element

    class Position:
        def make_position(self, node):
            def __init__(self):
                """Create an initially empty binary tree."""
                self.root = None
                self.size = 0

            def root(self):
                """Return the root Position of the tree( or None if tree is empty)."""
                return self.make_position(self.root)

            def add_root(self, e):
                """Place element e at the root of an empty tree and return new Position.
                Raise ValueError if tree nonempty."""
                if self.root is not None:
                    raise ValueError("Root Exist")
                self.size = 1
                self.root = self.Node(e)
                return self.make_position(self.root)

I'am a beginner with python and python data structure. How can I call at the end of file .py the methods add_root and print this method to see the element in root node? I tried to write

root = Tree.Position()
print(root.make_position(root))
root = Tree.Position.make_position()
print(root.make_position(root))

but the interpreter return an AttributeError

Answer 1

It's not very typical to define classes within other classes. I would recommend defining Tree, Node, and Position separately and then including those objects within the classes that require them. Also, it doesn't make much sense to define functions inside other functions. Functions should be defined independently from each other. Something like this:

class Tree:
    def __init__(self, root=None):
        self.root = root
    def print_values(self, root):
        if root == None: 
            return
        self.print_values(self.root.left)
        print root.data
        self.print_values(self.root.right)
    #Define other tree operations that you want to perform here

class Node:
    def __init__(self, data=0, left=None, right=None):
        self.data = data
        self.left=left
        self.right=right

#Create a root node
root = Node(0)
#Create a tree with the root node
m_tree = Tree(root)
#Add a left and right node to the root
left_node = Node(3)
right_node = Node(4)
root.left = left_node
root.right = right_node
m_tree.print_values(m_tree.root)