Step 7.2 - Learn Conditional Statements - the else statement

Theory: the else statement

We learned, that the if statement must always result in True and only then Python can execute actions suitable for that event. But, what if we want to execute another set of actions in case the if condition results in False?
The else statement allows us to achieve this intention.

Example

Let’s modify the previous example:

A = 1
B = 2
if A == B:
    print("A equals to B event happened")
    D = A + B
else:
    print("A does NOT equal to B")

In the above example we do following:

• Create two variables A and B and check if they are equal on the 3rd line.
• Since they are not equal, lines 4 and 5 won’t be executed.
• Therefore Python checks if there is else statement, and we have it present on the 6th line.
• Python then executes line 6 and prints text since it’s inside the else block.

The else statement cannot be used alone without the if statement.

Python learn Conditionals - the if and else statements example visualized

Practice: the else statement

Let’s continue writing the calculator. We’re going to use the else statement as an indication that user didn’t enter a math operator we have expected +, -, *, /. Therefore we want to handle this situation and print Unknown operator.

Here are the guidelines:

• Re-use the code we wrote in Step 8
• Write the else statement, its block should just print Unknown operator
• The result should look like this:

    enter first number: 70
    enter second number: 7
    enter math operator (+, -, *, /): ^
    Unknown operator
  

Solution

number_1 = int(input('enter first number: '))
number_2 = int(input('enter second number: '))
operator = input('enter math operator (+, -, *, /): ')

if operator == '+':
    print('the result is:', number_1 + number_2)
else:
    print('Unknown operator')

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