Python not

The not keyword in Python is a logical operator used to negate a Boolean value or expression. If the expression evaluates to True, not converts it to False, and vice versa. It is often used to reverse conditions in decision-making statements like if.

Example 

is_raining = False

if not is_raining:

    print("It's not raining. You can go outside!")

Output:

It's not raining. You can go outside!

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Syntax

not expression

• expression: Any Boolean expression or value that can evaluate to True or False.

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Why Use not?

1. Negate Boolean Values: Reverse the result of a condition or Boolean value.
2. Simplify Logic: Make conditions more readable by expressing “not something.”
3. Control Flow: Helps define alternative conditions in decision-making constructs.

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Common Examples

1. Negating a Boolean Value

is_logged_in = False

if not is_logged_in:

    print("You need to log in!")

Output:

You need to log in!

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2. Negating an Expression

x = 5

if not x > 10:

    print("x is not greater than 10")

Output:

x is not greater than 10

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3. Using not in Function Calls

def is_even(number):

    return number % 2 == 0

if not is_even(5):

    print("The number is odd")

Output:

The number is odd

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4. Combining not with Logical Operators

age = 16

has_permission = False

if not (age >= 18 or has_permission):

    print("Access denied")

Output:

Access denied

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5. Using not with Lists

shopping_list = []

if not shopping_list:

    print("The shopping list is empty")

Output:

The shopping list is empty