2.5. If-Else Statements

If you want to execute code if a condition is False, we can use the else statement.

The else statement is always used after an if statement. The structure of an if-else statement is:

if condition:
    # code you execute if condition is true
else:
    # code you execute if condition is false

Take note of the following:

• else is a keyword

• The code inside the else statement only executes if the condition is False. The else statement doesn’t have a condition after it. (Remember: Else is lonely. Else is by itself!)

• : is placed after the else

• Similar to the if statement, the code inside the else statement must be indented.

Here is an example of a simple if-else statement.

x = 1

if x < 0:
    print("x is a negative number")
else:
    print("x is a positive number")

In this example the condition is False so the second print statement runs.

Question 1

What do you think the output of the following code will be?

current_speed = 45
speed_limit = 40

if current_speed > speed_limit:
    print('You are speeding! {}km/h is above the speed limit of {}km/h. Slow down!'.format(current_speed, speed_limit))
else:
    print('You are travelling within the speed limit.')

Solution

You are speeding! 45km/h is above the speed limit of 40km/h. Slow down!

The condition in the if statement evaluates to True so the code indented in the if statement will execute, but the code under the else will not.

Note that this code also using string formatting.

Question 2

What do you think the output of the following code will be?

time = 6

print("I'm hungry.")

if time == 6:
    print("It's dinner time!")
else:
    print('Dinner will be soon...')

print('I hope we get pizza for dinner!')

Solution

Solution is locked

Code challenge: Elevator

Implement the algorithm illustrated in the diagram below in Python. Pay close attention to the indentation.

Solution

Solution is locked

Code challenge: Odd Even

Write a program that asks the user for an integer and then displays whether the number is odd or even.

Example 1

Enter a number: 1
This number is odd

Example 2

Enter a number: 2
This number is even

Hint

Use the modulus operator % to returns the remainder.

• When even numbers are divided by 2 the remainder is 0

• When odd numbers are divided by 2 the remainder is 0

Solution

Solution is locked