What’s interesting to do with booleans, and expressions that return a boolean in particular, is that we can make decisions and take different roads depending on their True or False value.

In Python we do so using the if statement:

condition = True

if condition == True:
    # do something

When the condition test resolves to True, like in the above case, its block gets executed.

What is a block? A block is that part that is indented one level (4 spaces usually) on the right:

condition = True

if condition == True:
    print("The condition")
    print("was true")

The block can be formed by a single line, or multiple lines as well, and it ends when you move back to the previous indentation level:

condition = True

if condition == True:
    print("The condition")
    print("was true")

print("Outside of the if")

In combination with if you can have an else block, that’s executed if the condition test of if evaluates to False:

condition = True

if condition == True:
    print("The condition")
    print("was True")
else:
    print("The condition")
    print("was False")

And you can have different linked if checks with elif, that’s executed if the previous check evaluated to False:

condition = True
name = "Roger"

if condition == True:
    print("The condition")
    print("was True")
elif name == "Roger":
    print("Hello Roger")
else:
    print("The condition")
    print("was False")

The second block in this case is executed if condition is False, and the name variable value is “Roger”.

In an if statement you can have just one if and one else, but multiple elif checks:

condition = True
name = "Roger"

if condition == True:
    print("The condition")
    print("was True")
elif name == "Roger":
    print("Hello Roger")
elif name == "Syd":
    print("Hello Syd")
elif name == "Flavio":
    print("Hello Flavio")
else:
    print("The condition")
    print("was False")

if and else can also be used in an inline format, which lets us return one value or another based on a condition.

Example:

a = 2
result = 2 if a == 0 else 3
print(result) # 3

Lessons in this unit:

0:	Introduction
1:	▶︎ Control statements
2:	Ternary operator
3:	Loops
4:	Lists
5:	List comprehensions
6:	How to create a list from a string
7:	Tuples
8:	Dictionaries
9:	Sets