Making Decisions

1. One equals stores, two equals compares

This is the number-one beginner mix-up, so get it straight first:

• = stores. age = 13 puts the value 13 into the variable age.
• == compares. age == 13 asks a question, “is age equal to 13?”, and answers True or False.

age = 13        # change this with the control below
print(age == 13)  # is age equal to 13?
print(age == 10)  # is age equal to 10?

2. Comparison operators and Booleans

Every comparison gives back a Boolean, either True or False.

Try reading each of these and deciding the answer before you check: is 5 == 5? is 3 != 3? is 9 > 4?

3. The if statement

An if runs the indented code only when its condition is True. Two things matter: the colon at the end of the if line, and the indentation (4 spaces) that marks the body.

age = 15
if age >= 13:
    print("You are old enough.")

If the condition is False, the indented line simply does not run, so nothing is printed.

4. if / else

else covers everything the if did not. Exactly one of the two blocks runs.

score = int(input("What did you score on the test? "))

if score >= 50:
    print("You passed! Well done.")
else:
    print("Not quite, have another go.")

5. Worked example: secret-word game

This pulls Lesson 1 (input()) and today’s lesson (if / else with ==) together.

secret = "python"
guess = input("Guess the secret word: ")

if guess == secret:
    print("Correct! You got it.")
else:
    print("Nope, try again.")

Notice we compare with == (a question), never = (which would try to store).

6. Quick check Part 1 of 2

Six quick questions. This is half of completing the module. The coding task below is the other half.