is — Intermediate Playground

Identity operator; tests whether two variables reference the same object

Python Playground

# Singletons: use 'is'
print(True is True)
print(None is None)

# Small integer caching (-5 to 256)
a = 256
b = 256
print(f"256 is 256: {a is b}")  # True (cached)

a = 257
b = 257
print(f"257 is 257: {a is b}")  # May be False!

# String interning
s1 = "hello"
s2 = "hello"
print(f'"hello" is "hello": {s1 is s2}')  # Usually True (interned)

# == can be overridden, is cannot
class AlwaysEqual:
    def __eq__(self, other):
        return True

obj = AlwaysEqual()
print(f"obj == 42: {obj == 42}")
print(f"obj is 42: {obj is 42}")

Output

Click "Run" to execute your code

'is' is a pointer comparison that cannot be overridden. '==' calls __eq__ which can return anything. Use 'is' for singletons, '==' for value comparison.

Challenge

Try modifying the code above to explore different behaviors. Can you extend the example to handle a new use case?

View all Intermediate examples for is