Application of Recursive Data: Decision Trees

class Tree:
    def __init__(self, cargo, left=None, right=None):
        self.cargo = cargo
        self.left = left
        self.right = right

def yes(ques):
    ans = str(input(ques)).lower()
    return ans[0] == "y"

def walkDecisionTree(root):
        while root.left is not None:
            prompt = root.cargo + "? "
            if yes(prompt):
                root = root.right
            else:
                root = root.left
        answernode = root
        return answernode

def addNewQ(leaf):
        oldguess= leaf.cargo
        prompt  = "What is the animal's name?"
        newanimal  = input(prompt)
        prompt  = "What question would distinguish a {0} from a {1}? "
        question = input(prompt.format(newanimal, oldguess))
        leaf.cargo = question
        prompt = "If the animal were {0} the answer would be? "
        if yes(prompt.format(newanimal)):
            leaf.left = Tree(oldguess)
            leaf.right = Tree(newanimal)
        else:
            leaf.left = Tree(newanimal)
            leaf.right = Tree(oldguess)


def animalQnA(root):
    # Loop until the user quits
    while True:
        print()
        if not yes("Are you thinking of an animal? "): break
        answernode = walkDecisionTree(root)
        prompt = "Is it a " + answernode.cargo + "? "
        if yes(prompt):
            print("I rule!")
        else:
            addNewQ(answernode)


def printAllAnimals(t):
    global animalCounter
    if t.left == None:
        print(animalCounter, t.cargo)
        animalCounter += 1
    else:
        printAllAnimals(t.left)
        printAllAnimals(t.right)

root = Tree("Have fur",Tree("bird"),Tree("cat"))
animalQnA(root)
print("Q&A is over: Here are animals")
animalCounter = 0
printAllAnimals(root)