Booleans are commonly used as a True or False statement. The simplest example would be comparing two numbers, is 1 greater than 2?

print( 1 > 2 )

Python will happily tell you that this is a false statement. In Python (and in computer programming in general), you will need to use boolean statements frequently in various scenarios that we will explore here. Let’s take a look at several examples:

Are these numbers equal?

print( 1 == 2 )
print( 2 < 1 )

These will all return False. Note that False is one of the few capitalized keywords in Python. A few examples that will return True are:

print( 2 == 2 )
print( 5 > 1 )
print( 1 < 3 )

We can use booleans to drive our logic in our code like so:

myVar = True

if myVar:
    print("It is true!")
else:
    print("Its false!")

Try changing the value of myVar to False and run the code. Note that we will dive deeper into if..else statements in future lessons.

A very handy use of booleans is to see if a variable is set. You will use this quite frequently when you are querying APIs - sometimes you will attempt to do something like create a user account and you will need to see if the API returned an error. This would be a perfect True or False scenario. Let’s take a look at how we can get a True or False result based on if a variable has a value or not:

myVar = "I am a string and I will return True!"
anotherVar = ""

print( bool(myVar) )
print( bool(anotherVar) )

Here we are assigning to string variables. The first has text inside the string and the second is empty. If we cast these variables to a boolean, the first returns True and the second returns False. Let’s say for example we have a variable named “apiError”, and we want to display an error message if something goes wrong in our code. We can do that like this:

apiError = ""

if apiError:
    print("There was an error with the API! Error message: " + apiError)
else:
    print("No error was found")

Try editing the apiError variable and write some error code.

Empty values generally return False:

print( bool ( "" ) )
print( bool ( 0 ) )

Even lists, tuples, sets and dictionaries:

print( bool ( [] ) ) # List
print( bool ( () ) ) # Tuple
print( bool ( {} ) ) # Set or dictionary

If you place a value in any of these objects then they will then return true:

print( bool ( [ "item" ] ) ) # List
print( bool ( ( "item" ) ) ) # Tuple
print( bool ( { "item" } ) ) # Set

Functions can return a boolean as well:

def my_function(x):

def my_function(x):
    if x > 5:
        return True
    else:
        return False
        
print( my_function(1) )
print( my_function(3) )
print( my_function(6) )
print( my_function(7) )

We can also get a boolean result if we check to see if a variable is of a certain type. Let’s say we want to see if a variable is of the type int:

myVar = 5
print( isinstance(myVar, int) )

As you can see Booleans are a critical concept for you to understand. Take some time and practice what you’ve learned in this lesson to make sure you fully understand before moving on.

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