Python Booleans

Python Booleans: True, False, and Truthy Evaluations

A Python boolean (bool) represents one of two truth values: True or False (always capitalized). Booleans drive every if condition, while loop, and filter check in your program.

Comparison operators (==, !=, <, >, <=, >=) and membership checks (in, is) all return a boolean value. Logical operators (and, or, not) combine multiple boolean checks together.

Boolean Comparisons and Truthiness

Python lets you test any object directly inside an if statement without calling bool(). Empty values evaluate to False, while populated values evaluate to True.

items_in_cart = ["keyboard", "mouse"]
coupon_code = ""

has_items = len(items_in_cart) > 0
print(has_items)                # True
print(bool(coupon_code))        # False

if items_in_cart and not coupon_code:
    print("Ready for standard checkout.")

Short-Circuit Evaluation

Python stops evaluating and as soon as it sees a falsy value, and stops or as soon as it sees a truthy value. You can rely on this to guard against None or empty lists before accessing attributes.

user = None
if user is not None and user["active"]:
    print("Welcome back")

Common Mistakes to Avoid

• Writing lowercase true or false: Python raises NameError unless you capitalize True and False.
• Using if flag == True:: Write if flag: directly, or if flag is True: only when distinguishing True from 1.
• Confusing if count: when 0 is valid: Checking if count: treats 0 as missing; write if count is not None: when zero is a valid number.

Frequently Asked Questions

What values are falsy in Python?

False, None, 0, 0.0, "", [], (), {}, and set() are all falsy. Custom classes can also define __bool__ or __len__.

What is the difference between == and is?

== checks whether two objects have equal values, while is checks whether both variables point to the exact same object in memory.

Why does True + True equal 2?

Because bool inherits from int, where True has numeric value 1 and False has value 0. This lets you write sum(x > 10 for x in scores) to count matches.