Python Program to Display the Nodes of a Tree using BFS Traversal

When it is required to display the nodes of a tree using the breadth first search traversal, a class is created, and it contains methods to set the root node, add elements to the tree, search for a specific element, perform ‘bfs’ (breadth first search) and so on. An instance of the class can be created to access and use these methods.

Below is a demonstration of the same −


 Live Demo

class Tree_struct:
   def __init__(self, data=None):
      self.key = data
      self.children = []

   def set_root(self, data):
      self.key = data

   def add_node(self, node):

   def search_node(self, key):
      if self.key == key:
         return self
      for child in self.children:
         temp = child.search_node(key)
         if temp is not None:
            return temp
      return None

   def bfs_operation(self):
      queue = [self]
      while queue != []:
         popped = queue.pop(0)
         for child in popped.children:
         print(popped.key, end=' ')

my_instance = None

print('Menu (assume no duplicate keys)')
print('add <data> at root')
print('add <data> below <data>')

while True:
   my_input = input('What operation would you do ? ').split()

   operation = my_input[0].strip().lower()
   if operation == 'add':
      data = int(my_input[1])
      new_node = Tree_struct(data)
      suboperation = my_input[2].strip().lower()
      if suboperation == 'at':
         my_instance = new_node
      elif suboperation == 'below':
         position = my_input[3].strip().lower()
         key = int(position)
         ref_node = None
         if my_instance is not None:
            ref_node = my_instance.search_node(key)
         if ref_node is None:
            print('No such key')

   elif operation == 'bfs':
      if my_instance is None:
         print('The tree is empty')
         print('Breadth First Search traversal is : ', end='')

   elif operation == 'quit':


Menu (assume no duplicate keys)
add <data> at root
add <data> below <data>
What operation would you do ? add 6 at root
What operation would you do ? add 4 below 6
What operation would you do ? add 9 below 4
What operation would you do ? bfs
Breadth First Search traversal is : 6 4 9
What operation would you do ? quit


  • The ‘Tree_struct’ class with required attributes is created.

  • It has an ‘init’ function that is used to create an empty list.

  • A ‘set_root’ method is defined that helps set the root value of the binary tree.

  • It has an ‘add_node’ method that helps add elements to the tree.

  • A method named ‘search_elem’ is defined, that helps search for a specific element.

  • A method named ‘bfs_operation’ is defined, that helps perform breadth first search traversal on the tree.

  • An instance is created and assigned to ‘None’.

  • The user input is taken for the operation that needs to be performed.

  • Depending on the user’ choice, the operation is performed.

  • Relevant output is displayed on the console.

Updated on: 17-Apr-2021


Kickstart Your Career

Get certified by completing the course

Get Started