用python写一个二叉树

下面是一个简单的二叉树的Python实现：

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

class BinaryTree:
    def __init__(self, root):
        self.root = Node(root)

    def print_tree(self, traversal_type):
        if traversal_type == "preorder":
            return self.preorder_print(tree.root, "")
        elif traversal_type == "inorder":
            return self.inorder_print(tree.root, "")
        elif traversal_type == "postorder":
            return self.postorder_print(tree.root, "")

    def preorder_print(self, start, traversal):
        if start:
            traversal += (str(start.value) + "-")
            traversal = self.preorder_print(start.left, traversal)
            traversal = self.preorder_print(start.right, traversal)
        return traversal

    def inorder_print(self, start, traversal):
        if start:
            traversal = self.inorder_print(start.left, traversal)
            traversal += (str(start.value) + "-")
            traversal = self.inorder_print(start.right, traversal)
        return traversal

    def postorder_print(self, start, traversal):
        if start:
            traversal = self.postorder_print(start.left, traversal)
            traversal = self.postorder_print(start.right, traversal)
            traversal += (str(start.value) + "-")
        return traversal

# Create a binary tree with root node as 1
tree = BinaryTree(1)

# Add nodes to the binary tree
tree.root.left = Node(2)
tree.root.right = Node(3)
tree.root.left.left = Node(4)
tree.root.left.right = Node(5)
tree.root.right.left = Node(6)
tree.root.right.right = Node(7)

# Print the binary tree in different traversal orders
print(tree.print_tree("preorder"))
print(tree.print_tree("inorder"))
print(tree.print_tree("postorder"))

输出：

1-2-4-5-3-6-7-
4-2-5-1-6-3-7-
4-5-2-6-7-3-1-

这里实现了一个简单的二叉树，并且提供了三种不同的遍历方式：前序遍历、中序遍历和后序遍历。可以根据需要进行选择。