In what cases is None used in Python?

In Python, the value None is used to denote the absence of a value or a null value. It is a special object that is often used:

• For initializing variables when a value is not yet set.
• As a return value of a function that does not explicitly return anything.
• To check whether a parameter was passed or set.
• As a marker for missing data in structures.

Example:

def find_user(id):
    if id in database:
        return database[id]
    else:
        return None  # User not found

user = find_user(10)
if user is None:
    print("User not found")

None is the only object of type NoneType, and comparisons should be made using is, not ==.