Boolean Introduction

In Python, booleans are a type with two values, True or False. They can be operated on and queried with functions like if, and, or. Python also has a sense of truthy and falsey values, values that will act as true or false when given to if statements.

Working with Booleans

Python uses if, elif, and else to execute code based on boolean values. if and elif preceede an expression that evaluates to a boolean value, and execute the code indented below them if the value is True. else blocks of code will execute if all ifs and elifs failed.

if True:
    print('True')
elif False:
    print('Won't Print')
else:
    print('Won't Print')

Python uses the words and, or, and not for logical and, or, and not, as opposed to symbols like &.

True and True
# True
False or True
# True
not False and True
# True
True and False
# False

Boolean values can be assigned to variables and returned from functions just like any object.

true_variable = True
false_variable = False

true_variable and true_variable
# True

false_variable or false_variable
# False

def returns_true():
    return True

returns_true()
# True

Truthy and Falsey

Boolean operators can also work on non boolean values. Usually empty objects will evaluate to False, while objects that aren’t empty will evaluate to True.

  • Strings: “” == False, any string over length 0 == True
  • Lists: [] == False, any list over length 0 == True
  • Integers: 0 == False, any other number is True
  • None: None will evaluate to False, this is helpful when testing for any return value

Truthy and falsey values are useful for checking for the existence of objects.