Logical Operators

Logical operators combine boolean expressions.

age = 20
has_id = True
print(age >= 18 and has_id)     # True
print(age < 18 or has_id)       # True
print(not has_id)               # False

Truth Table

Short-Circuit Evaluation

Python stops evaluating as soon as the result is determined — and returns the actual operand value, not just True/False.

def check():
    print("check() called")
    return True

print(False and check())   # False -- check() never runs
print(True or check())     # True  -- check() never runs

# and/or return an operand, not necessarily a bool
print(0 or "default")      # 'default' (0 is falsy, so the second operand is returned)
print("hi" and "bye")      # 'bye' (both truthy, returns the last one)

Truthy and Falsy Values

Falsy: 0, 0.0, "", [], (), {}, None, False. Everything else is truthy.

if []:
    print("won't print")
if [1]:
    print("prints — non-empty list is truthy")