Boolean Logic

Python · Reference cheat sheet

📋 Overview

Boolean logic deals with True and False. You use it in if conditions, loops, and filters. Python’s operators are and, or, and not (words, not && / ||).

🔧 Core concepts

Comparisons return booleans. Many other values are truthy or falsy when used in conditions (see related note).

💡 Examples

Comparisons:

age = 18
print(age >= 18)   # True
print(age == 21)   # False
print(age != 0)    # True

and / or / not:

has_ticket = True
is_weekend = False

print(has_ticket and is_weekend)  # False
print(has_ticket or is_weekend)   # True
print(not is_weekend)             # True

if with boolean expressions:

temp_c = 22
raining = False

if temp_c > 20 and not raining:
    print("Nice walk weather")
elif raining:
    print("Take an umbrella")
else:
    print("Maybe stay in")

Short-circuit evaluation:

x = 0
# Right side is skipped because left is False
print(x != 0 and (10 / x > 1))  # False, no ZeroDivisionError

name = ""
label = name or "guest"
print(label)  # guest

⚠️ Pitfalls

• and / or return one of the operands, not always a strict bool.
• == vs is: use == for values; is for identity (None is the common exception).
• 1 < x > 0 is valid chaining — read carefully.
• Do not write if flag == True: — prefer if flag:.

🔗 Related

• none_and_truthy.md
• variables.md
• indentation.md
• truthiness.md