Exercise #23, using a binary tree

car.py

class TreeNode:
  def __init__(self, content):
    self.content = content
    self.yes = None
    self.no = None

  def is_question(self):
    return (self.yes != None or self.no != None)

# Prepare the decision tree

root = TreeNode('Is the car silent when you turn the key?')
root.yes = TreeNode('Are the battery terminals corroded?')
root.no = TreeNode('Does the car make a clicking noise?')

root.yes.yes = TreeNode('Clean terminals and try starting again.')
root.yes.no = TreeNode('Replace cables and try again.')

root.no.yes = TreeNode('Replace the battery.')
root.no.no = TreeNode('Does the car crank up but fail to start?')
root.no.no.yes = TreeNode('Check spark plug connections.')

root.no.no.no = TreeNode('Does the engine start and then die?')
root.no.no.no.yes = TreeNode('Does your car have fuel injection?')
root.no.no.no.yes.yes = TreeNode('Get it in for service.')
root.no.no.no.yes.no = TreeNode('Check to ensure the choke is opening and closing.')

#  Now we can start asking questions

current_node = root

while current_node:
  if current_node.is_question():
    answer = input(current_node.content + ' ')
    if answer.lower()[0] == 'y':
      current_node = current_node.yes
    else:
      current_node = current_node.no
    if current_node is None:
      print("I don't know what's wrong.  Good luck!")
  else:
    print(current_node.content)
    current_node = None