DFSpreorder.py

def preorder(root,visited):
 	if root: #check if node exits
 		visited.append(root.data) #append node value to visted stack (V)
 		visited=preorder(root.left,traversal) #go to left subtree (L)
 		visited=preorder(root.right,traversal) #go to right subtree (R)
 	return visited #return visited stack
preorder(root,[]) #call preorder function with visited stack