What is the role of the 'is' operator in programming languages, and what is it used for?

In Python, the is operator is used to check whether two variables refer to the same object in memory, i.e., it checks object identity.

Example:

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

print(a is b)  # True, because b refers to the same object
print(a is c)  # False, because c is a different object with the same content

Thus, is checks not for value equality, but whether both variables refer to the same object.