Programming Fundamentals › Programming Basics

Boolean

A true/false value.

Also known as: bool, boolean value, true false, Boolean type

A boolean is a value that’s either true or false, named after the mathematician George Boole. It’s the result of a question (“is the user an admin?”) and what conditions act on.

is_admin = True
age = 20
can_vote = age >= 18         # True: comparisons produce booleans

Operators

if age >= 18 and has_id:
    allow()

and/or stop early once the answer is known (short-circuit evaluation).

Habits

• Name booleans as questions: is_active, has_paid, can_edit (naming).
• Don’t compare to True: write if is_active:, not if is_active == True:.
• Return the condition directly instead of if x: return True else: return False: return x > 0.
• Beware of truthiness. Many languages let non-booleans act like true or false (an empty string, 0), and the rules differ (truthy and falsy).
• Strings aren’t booleans: "false" is truthy in most languages.
• A boolean column in a database can also be NULL, a third state (NULL in SQL).

Too many boolean flags often hide a better model, such as one status field.