If not true means the ‘not operator‘ is used in the if statements in Python. The ‘not’ is a Logical operator in Python that will return True if the expression is False.
if not var
If var is True, then not will evaluate as false, otherwise, True.
Example If not true in Python
Simple Python not-operator example with if statement.
x = 10
if not x > 0:
print("x is not greater then 0")
else:
print("x is greater then 0")
Output: As x>0 is False, so not-operator evaluated as True.

Python example if not with ‘in’
The elements that evaluated False as using ‘not’ did not display in the console.
a_List = [5, 10, 15, 20, 25, 30]
for a in a_List:
if not a in (10, 25):
print("List Item: ", a)
Output:

Do comment if you have any doubts or suggestions on this Python basic tutorial.
Note: IDE: PyCharm 2021.3 (Community Edition)
Windows 10
Python 3.10.1
All Python Examples are in Python 3, so Maybe its different from python 2 or upgraded versions.

Degree in Computer Science and Engineer: App Developer and has multiple Programming languages experience. Enthusiasm for technology & like learning technical.