Python If NOT

We can use logical not operator with Python IF condition. The statements inside if block execute only if the value(boolean) is False or if the value(collection) is empty.

Syntax of if statement with not

The syntax of Python If statement with NOT logical operator is

if not value:
    statement(s)

where not value part is the condition of the if statement, and the value could be of type boolean, string, list, dict, set, tuple, etc.

If value is of boolean type, then NOT acts a negation operator. If value is False, not value would be True, and the statement(s) in if-block will execute. If value is True, not value would be False, and the statement(s) in if-block will not execute.

If value is of type string, then statement(s) in if-block will execute if string is empty.

If value is of type list, then statement(s) in if-block will execute if list is empty. The same explanation holds for value of other collection datatypes: dict, set and tuple.

In summary, we can use if not expression to conditionally execute a block of code only if the value is empty or False.

Examples

1. Python "if not" with Boolean

In this example, we will use Python not logical operator in the boolean expression of Python IF statement.

Python Program

a = False

if not a:
    print('a is false.')

Since a is False, not a becomes True. And as the condition of if statement becomes True, the statements inside the if-block execute.

Output

a is false.

2. Python "if not" with String

In this example, we will use Python if not expression to print the string only if the string is not empty.

Python Program

string_1 = ''

if not string_1:
    print('String is empty.')
else:
    print(string_1)

string_1 is empty.
The boolean equivalent of an empty string is False. And not string_1 becomes True.
The condition of if-statement is True. Therefore, the statements inside the if-block execute.

Output

String is empty.

3. Python "if not" with List

In this example, we will use Python if not expression to print the list only if the list is not empty.

Python Program

a = []

if not a:
    print('Given list is empty.')
else:
    print(a)

The variable a is assigned with an empty list.
The boolean equivalent of an empty list is False. And not a becomes True.
The condition of if-statement is True. Therefore, the statements inside the if-block execute.

Output

Given list is empty.

4. Python "if not" with Dictionary

In this example, we will use Python if not expression to print the dictionary only if the dictionary is not empty.

Python Program

a = dict()

if not a:
    print('Given dictionary is empty.')
else:
    print(a)

The variable a is assigned with an empty dictionary.
The boolean equivalent of an empty list is False. And not a becomes True.
The condition of if-statement is True. Therefore, the statements inside the if-block execute.

Output

Given dictionary is empty.

5. Python "if not" with Set

In this example, we will use Python if not expression to print the set, only if the set is not empty.

Python Program

a = set({})

if not a:
    print('Set is empty.')
else:
    print(a)

The variable a is assigned with an empty set.
The boolean equivalent of an empty set is False. And not a becomes True.
The condition of if-statement is True. Therefore, the statements inside the if-block execute.

Output

Set is empty.

6. Python "if not" with Tuple

In this example, we will use Python if not expression to print the tuple, only if the tuple is not empty.

Python Program

a = tuple()

if not a:
    print('Tuple is empty.')
else:
    print(a)

The variable a is assigned with an empty tuple.
The boolean equivalent of an empty list is False. And not a becomes True.
The condition of if-statement is True. Therefore, the statements inside the if-block execute.

Output

Tuple is empty.

Video Tutorial on Python If not

In the following YouTube video, the explanation for if not statement with syntax, and examples is given.

https://youtu.be/LDD4orMWXxo

Summary

In this tutorial of Python Examples, we learned to use NOT logical operator along with if conditional statement, with the help of well detailed examples programs.