Identity Checks

In Python, the is and is not operators are used to check the identity of objects. Unlike the == operator, which checks if two variables have the same value, the is operator checks if two variables refer to the exact same object in memory.

Basic usage of is:

a = [1, 2, 3]
b = a
c = [1, 2, 3]

print(a is b)  # Output: True
print(a is c)  # Output: False

In this example, a and b refer to the same list object, so a is b returns True. However, a and c are different list objects with the same values, so a is c returns False.

Basic Usage of is not:

x = 5
y = 5
z = 10

print(x is not y)  # Output: False
print(x is not z)  # Output: True

Here, x and y refer to the same integer object (due to Python's optimizations for small integers), so x is not y returns False. x and z are different objects, so x is not z returns True.

Identity checks are particularly useful when you want to determine if two variables are pointing to the same object in memory, rather than just having the same value.