Else statement

Setting conditions is a pretty popular and useful tool in programming. However, sometimes just to check if a condition is true or not might not be enough. Let's say, you don't want a piece of code to execute if your condition is false, but, if that's the case, there is another piece of code you do want to execute. For situations like this Python has another powerful tool about which we're gonna learn in this topic!

Simple if-else

An if-else statement is another type of conditional expression in Python. It differs from an if statement by the presence of the additional keyword else. The block of code that else contains executes when the condition of your if statement does not hold (the Boolean value is False). Since an else statement is an alternative for an if statement, only one block of code can be executed. Also, else doesn't require any condition:

if today == "holiday":
    print("Lucky you!")
else:
    print("Keep your chin up, then.")

Note that the 4-space indentation rule applies here too.

As you may soon find out, programmers do like all sorts of shortcuts. For conditional expressions, there's a trick as well – you can write an if-else statement in one line. This is called a ternary operator and it looks like this:

print("It’s a day now!" if sun else "It’s a night for sure!")

Or, more generally:

first_alternative if condition else second_alternative

It's a matter of convenience, but remember that the code you create should still be readable.

Nested if-else

It should be mentioned that if-else statements can be nested the same way as if statements. An additional conditional expression may appear after the if section as well as after the else section. Once again, don't forget to indent properly:

if x < 100:
    print('x < 100')
else:
    if x == 100:
        print('x = 100')
    else:
        print('x > 100')
    print('This will be printed only because x >= 100')

Summary

In this topic, we've learned about one more type of conditional expression: if-else statement. Let's go through the main points again:

• the keyword else is used to give an alternative;
• it will be executed in case if statement isn't;
• it doesn't require any condition;
• if-else statements can be nested.

That's it! Now you are ready not only to set conditions but also to consider different alternatives. Congratulations!