python - 在python二叉树结构中创建根节点

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))

但是解释器返回一个 AttributeError

Answer 1

在其他类中定义类并不常见。我建议单独定义 Tree、Node 和 Position，然后将这些对象包含在需要它们的类中。此外，在其他函数中定义函数也没有多大意义。函数的定义应该相互独立。像这样的事情:

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)