not

Updated March 16, 2026 · Keywords

keyword boolean operator logical

The not keyword is a logical negation operator in Python. It returns the boolean opposite of its operand’s truthiness — True becomes False and vice versa.

Syntax

result = not expression

How It Works

Python’s not always returns a boolean value (True or False), unlike some languages where ! might return the original value. The operator evaluates the truthiness of its operand using the same rules Python uses throughout the language.

# Basic negation
print(not True)
# False

print(not False)
# True

# With non-boolean values - checks truthiness
print(not 0)
# True

print(not 1)
# False

print(not "")
# True

print(not "hello")
# False

print(not None)
# True

Truthiness Rules

Python considers these values falsy:

None
False
Zero: 0, 0.0, 0j, Decimal(0), Fraction(0, 1)
Empty sequences: "", [], (), {}
Objects with __bool__() returning False or __len__() returning 0

Everything else is truthy.

# Numbers
print(not 0)      # True - zero is falsy
print(not 42)     # False - non-zero is truthy

# Strings
print(not "")     # True - empty string is falsy
print(not "x")    # False - non-empty is truthy

# Collections
print(not [])     # True - empty list is falsy
print(not [1])    # False - non-empty list is truthy

# None
print(not None)   # True

Common Use Cases

Negating conditions

is_logged_in = False

if not is_logged_in:
    print("Please log in")
# Please log in

user = None

if not user:
    print("No user found")
# No user found

Double negation

Sometimes you need to convert a truthy/falsy value to an explicit boolean:

value = "hello"

# Using not not to get boolean
is_truthy = not not value
print(is_truthy)
# True

value = ""

is_truthy = not not value
print(is_truthy)
# False

# Modern alternative - bool()
is_truthy = bool(value)
print(is_truthy)
# False

Combining with other operators

x = 5

# not with comparison
print(not x > 10)
# True

# not with in
languages = ["python", "rust", "go"]

if "javascript" not in languages:
    print("Not found")
# Not found

# not with isinstance
value = "hello"

if not isinstance(value, int):
    print("Not an integer")
# Not an integer

Guard patterns

def greet(user):
    if not user:
        return "Hello, stranger!"
    return f"Hello, {user}!"

print(greet("Alice"))
# Hello, Alice!

print(greet(""))
# Hello, stranger!

print(greet(None))
# Hello, stranger!

Precedence

The not operator has lower precedence than comparison operators but higher than and and or:

x = 5

# not binds tighter than and/or but looser than comparisons
result = not x > 0
print(result)
# False

# Parentheses can clarify intent
result = not (x > 0)
print(result)
# False

Operator precedence from highest to lowest:

not (unary)
and
or

# Demonstration
print(not True or True)
# True - (not True) is False, False or True is True

print(not (True or True))
# False - not True is False

Boolean Context

When not is used in a boolean context, the result is already a boolean, so no conversion happens:

result = not "hello"
if result:
    print("This won't execute")
# (nothing printed - result is False)

if not not "hello":
    print("This will execute")
# This will execute