Adventures in Machine Learning

Building and Implementing Binary Trees in Python

Introduction to Binary Trees

Binary trees are one of the fundamental concepts of computer science. They are used extensively in various algorithms like sorting, searching, and indexing.

Understanding binary trees is essential for any programmer, and this article will provide an in-depth understanding of binary trees.

Definition of a Binary Tree

A binary tree is a tree data structure where each node contains a maximum of two child nodes, known as left and right child nodes or the left-subtree and right-subtree. The parent object of these two child nodes is known as the root node of the tree.

The child nodes only have one parent node, and the root node does not have any parent object. In summary, a binary tree is made up of nodes connected by edges, where each node has two child nodes, except for leaf nodes that do not have child nodes.

Implementation of a Binary Tree in Python

In Python, we can implement a binary tree using a class. The class contains a constructor with references to the left and right child nodes, and it also stores the data value of the node.

We can traverse the tree using different methods such as preorder, inorder, and postorder. These traversal methods determine the order in which you visit each node.

Basic Terminologies in Binary Trees

Root Node

The root node is the topmost node in a binary tree. It is the first node in the tree and does not have any parent nodes.

All other nodes in the binary tree are children of the root node.

Parent Node

The parent node is a node that has at least one child node. Each node in the binary tree has only one parent node except the root node that does not have any parent object.

The leftChild and rightChild properties of a node point to its two child nodes.

Child Node

Child nodes of a parent node are the nodes that are connected to the parent node by an edge. A parent node can have zero to two child nodes.


An edge is the link between two nodes, connecting the parent node to its child node. The edge direction is from parent to child.

Internal Nodes

A node that has at least one child node is an internal node. These nodes are used to create a binary tree structure.

Leaf Node or External Nodes

A leaf node, also known as an external node, is a node that does not have any child nodes. These nodes are found at the end of the tree and do not have any further sub-trees.


Binary trees are an instrumental data structure for any programmer that deals with algorithms, especially for sorting, searching, and indexing. In summary, each node in a binary tree can have a maximum of two child nodes, known as left and right sub-trees.

It is easy to implement in Python, and the tree traversal methods determine the order of visiting each node in the tree. The properly described terminologies associated with binary trees are also crucial in building the correct tree structure and operations.

Implementing a Binary Tree in Python

Binary trees are a widely used data structure in computer science and programming. They are primarily used for efficient searching and sorting algorithms.

In this article, we will discuss how to create and implement a binary tree in Python, including creating node objects, adding children to nodes, and printing data in nodes and children.

Creating Node Objects

The first step in building a binary tree is to create a node object, which represents a single item in the tree. Each node contains a data field that stores the object or value being stored.

In Python, we can create BinaryTreeNode objects for each node in the tree. The BinaryTreeNode class would have a constructor function that takes in a parameter for the data being stored in the node, and the left and right child references.

Here is an example of creating a BinaryTreeNode class in Python:


class BinaryTreeNode:

def __init__(self, data): = data

self.leftChild = None

self.rightChild = None


In the above code, we have created a class called BinaryTreeNode that contains a constructor function that initializes the data field to the value passed in as the argument. The leftChild and rightChild references are also initialized to None in this example.

Adding Children to Nodes

Once we have created a node object, we can add child nodes to it. In a binary tree, each node can have a maximum of two child nodes a left child and a right child.

We can add these child nodes by updating the leftChild and rightChild references of a node object using the setLeftChild() and setRightChild() methods. Here is an example of how to create a binary tree by adding child nodes to a root node:


root = BinaryTreeNode(1)

root.leftChild = BinaryTreeNode(2)

root.rightChild = BinaryTreeNode(3)


In the above example, we first create a root node with a value of 1.

Then we add child nodes to the root by assigning new BinaryTreeNode objects to the leftChild and rightChild properties of the root node.

Printing Data in Nodes and Children

After we have created a binary tree, we may want to print the data stored in each node or the children of any node in the tree. We can do this using the print() function.

Here is an example of how to print data in a node and its children:






In the above example, we print the data stored in the root node, as well as the data stored in its left and right child nodes.


In summary, implementing a binary tree in Python involves creating node objects for each item in the tree, adding child nodes to each node object using the leftChild and rightChild references, and printing the data stored in nodes and their children. By understanding these topics, you will be able to create and work with binary trees in Python efficiently.

In conclusion, implementing binary trees in Python is important for programmers as they are an essential data structure used in various algorithms. The process involves creating node objects with a constructor function, adding child nodes, and printing data in nodes and children.

The binary tree structure consists of a root node, parent nodes, child nodes, edges, internal nodes, and leaf nodes. By understanding these concepts, programmers can efficiently create and use binary trees in their projects.

The importance of binary trees cannot be overemphasized, as they enable programmers to easily sort, search, and index data.