Boundary traversal of Binary tree

class Solution:
    def printBoundaryView(self, root):
        def l(root):
            if not root:return []
            ans,x=[],root
            while x:
                if not x.left and not x.right:
                    return list(ans)
                ans.append(x.data)
                if x.left:x=x.left
                else:x=x.right

        def r(root):
            if not root:return []
            ans,x=deque(),root
            while x:
                if not x.left and not x.right:
                    return list(ans)
                ans.appendleft(x.data)
                if x.right:x=x.right
                else:x=x.left
            return ans
        t=[]#for storing leaves not included root
        def preorder(x):# only store leaves
            if not x:return
            if not x.left and not x.right and x!=root:t.append(x.data)
            preorder(x.left)
            preorder(x.right)

        preorder(root)
        ans=[root.data]
        if root.left:
            ans+=l(root.left)
        ans+=t
        if root.right:
            ans+=r(root.right)
        return ans


#{
#  Driver Code Starts
#Initial Template for Python 3

# function should return a list containing the boundary view of the binary tree
#{
#  Driver Code Starts
import sys

import sys
sys.setrecursionlimit(100000)
#Contributed by Sudarshan Sharma
from collections import deque
# Tree Node
class Node:
    def __init__(self, val):
        self.right = None
        self.data = val
        self.left = None

# Function to Build Tree
def buildTree(s):
    #Corner Case
    if(len(s)==0 or s[0]=="N"):
        return None

    # Creating list of strings from input
    # string after spliting by space
    ip=list(map(str,s.split()))

    # Create the root of the tree
    root=Node(int(ip[0]))
    size=0
    q=deque()

    # Push the root to the queue
    q.append(root)
    size=size+1

    # Starting from the second element
    i=1
    while(size>0 and i<len(ip)):
        # Get and remove the front of the queue
        currNode=q[0]
        q.popleft()
        size=size-1

        # Get the current node's value from the string
        currVal=ip[i]

        # If the left child is not null
        if(currVal!="N"):

            # Create the left child for the current node
            currNode.left=Node(int(currVal))

            # Push it to the queue
            q.append(currNode.left)
            size=size+1
        # For the right child
        i=i+1
        if(i>=len(ip)):
            break
        currVal=ip[i]

        # If the right child is not null
        if(currVal!="N"):

            # Create the right child for the current node
            currNode.right=Node(int(currVal))

            # Push it to the queue
            q.append(currNode.right)
            size=size+1
        i=i+1
    return root


if __name__=="__main__":
    t=int(input())
    for _ in range(0,t):
        s=input()
        root=buildTree(s)
        obj = Solution()
        res = obj.printBoundaryView(root)
        for i in res:
            print (i, end = " ")
        print('')
# } Driver Code Ends