If Statement

Simple if Statement

In it's simplest form, an if statement looks like this:

if conditional_test:
    # do something

if conditional_test evaluates to True, then the indented code block is executed. If it evaluates to False, then the indented code block is skipped.

Python uses indentation to determine which lines of code are associated with the if statement. All indented lines after the if statement are considered part of the code block. The code block ends when the indentation returns to the same level as the if statement.

if conditional_test:
    # do something
    # do something else

# code block ends here

Let's see this in practice:

car = "BMW"

if car.lower() == "bmw":
    print("Your car is awesome!")

print("Have a nice day!")

with output:

Your car is awesome!
Have a nice day!

Try to change the value of car to something else and see what happens.

if-else Statement

A more elaborate form of the if statement is the if-else statement. It looks like this:

if conditional_test:
    # do something
else:
    # do something different

It allows you to specify an alternative action if the conditional_test evaluates to False.

For example,

car = "Mercedes"

if car.lower() == "bmw":
    print("Your car is awesome!")
else:
    print("Your car is okay...")

print("Have a nice day!")

produces output:

Your car is okay...
Have a nice day!

if-elif-else Statement

The if-elif-else statement allows you to specify multiple alternative actions. It's allowed to have multiple elif statements, but only one else statement.

if conditional_test_1:
    # do something
elif conditional_test_2:
    # do something different
elif conditional_test_3:
    # do something event more different
else:
    # do something else

We can now write more ellaborate classification of cars:

car = "Mercedes"

if car.lower() == "bmw":
    print("Your car is awesome!")
elif car.lower() == "mercedes":
    print("Your car is expensive!")
elif car.lower() == "ferarri":
    print("Your car is fast!")
else:
    print("Your car is okay...")

print("Have a nice day!")

Your car is expensive!
Have a nice day!

In this example, once car.lower() == "mercedes" evaluates to True, the rest of the elif statements, and the else statement, are skipped.

The else statement is optional. It is used to specify an action if none of the if or elif statements evaluate to True. And it must be the last statement in the if statement.