Touring Turing

1 What is 'Conditional Selection'

Learn It

  • One of the important aspects of a Turing machine, is the ability to change the tape, depending on what was written on some programmed cards.
  • So, for instance, if the Turing machine was at box 500 on the tape, if the symbol written there was a 1 - it would leave it and move to the next box. else if the symbol that was written there was a 0 the erase it and write in a 1, before moving on to the next box.

Learn It

  • This is know as Conditional Selection.
  • If you want to imagine using Conditional Selection in real life, think about a simple decision you might make before leaving the house in the morning.

If it is cold I will take my coat, else I'll leave it at home.

Code It

  • Let's try and code the above example using python.
  • Open IDLE and create a new script (Ctrl+n) called
  • We need to start by creating a variable to store whether it is cold or not.
  • On the first line of your script write the following line.
coldOutside = True
  • True is a type of data in Python.
  • Now we're going to start our conditional selection. Write this line next.
if coldOutside == True:
  • The double equals is known as a test for equality. In Python a single equals is used for assigning variables. A double equals tests if two things are the same.
  • The : is important. It tells the computer that we have finished stating the condition. In this case that coldOutside = True
  • Now hit Enter on your keyboard and stop.


  • The cursor has automatically been placed 4 spaces in, leaving what is known as significant whitespace where you are going to write your next line.
  • If you accidentally delete the whitespace (do it now), you can add it back in by using the Tab key on your keyboard.


  • Let's write the next line
if coldOutside == True:
    print('You had better take your coat')
  • Because the print() statement is written after the significant white space, it will only be executed if the line above it is True.
  • What happens if coldOutside isn't True?
  • We need to prepare for that as well.
if coldOutside == True:
    print('You had better take your coat')
    print('Leave your coat at home')
  • Notice that the else: has no whitespace before it.
  • The print() statement under the else: condition, only runs if coldOutside is not True
  • Ctrl+s and then F5 to save and run your script.
  • Now try changing the variable coldOutside from True to False

Badge It - Silver

  • Now it's your turn to write some conditional selection scripts. Make sure you use sensible variable names
  • Try the following:
    1. Write a script that prints out whether you should have a snack based on whether you are hungry or not.
    2. Write a script that prints out whether you should have a sleep or not based on whether you are tired or not.
    3. Write a script that prints out whether you should take a bus or not based on whether your journey is a long one.

2 More tests

Learn It

  • We can use conditional selection to test for pretty much anything, not just whether a variable is True or False.
  • We can test the value of any variable value we like.

Code It

  • Let's make a little chatbot.
name = 'Alice'
if name == 'Alice':
    print('Nice to meet you ' + name)
    print('I wanted to speak to Alice, not ' + name)
  • We can make this script a little more interactive by using input() like we did in the previous lesson
name = input('Hi, what is your name? ')
if name == 'Alice':
    print('Nice to meet you ' + name)
    print('I wanted to speak to Alice, not ' + name)
  • You can change what the script replies if you like.
  • Let's extend it a little. Add a second block of conditional selection to your script, underneath the first.
pets = input('Do you have any pets? ')
if pets == 'yes':
    print("That's nice. I love pets")
    print("That's a shame. You should buy a dog.")
  • Add a few more questions and responses of your own, to extend the chatbot.

Badge It - Gold

  • We can use Conditional Selection to make a quiz.
  • Have a look at the script below.
score = 0

userAnswer1 = input('What is the capital city of England?' )
if userAnswer1 == 'London':
    score = score + 1
  • The first line creates a variable called score and sets it to 0
  • This line
score = score + 1
  • adds 1 to the score. As it has whitespace before it, it only runs when the user gets the answer correct.
  • Add 4 more questions to your script.

3 Type Casting again

Learn It

  • It would be nice if we could print out the score at the end of the quiz.
  • There's a slight problem though.
  • Try this as the last line of code.
print('You scored ' + score)
  • Run through the quiz and see what happens.
  • The problem is the same as we experienced in the last lesson. The string 'You scored ' and the integer score are different types, and you can't concatenate different types in Python (Do you still remember what concatenate means).
  • This time we'll use the inbuilt function str().
  • This converts numbers to strings. So if the score was 6 it would convert it to '6'
  • Change your last line of code so it looks like the one below.
print('You scored ' + str(score))

Code It

  • Can you remember how to use int() to change a user's input into a number.
  • We could add some Maths questions to our script by using int()
  • Here's an example question, and the beauty of it is that we don't have to work out the answer ourselves.
answer6 = int(input('What is 7 multiplied by 8? '))
if answer6 == 7*8:
    score = score + 1

Badge It - Platinum

  • Now try adding 3 simple Maths questions to the quiz (addition, multiplication, subtraction or division (+,*,-,/))
  • Add another question 3 questions that asks the user to answer the same questions you answered for the The Platinum Badge on Week 1
Badge it!