What is the difference between is and ==?

== (value comparison):

Checks whether the values match between two objects:

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

print(a == b)  # True — values are the same

is (identity comparison):

Checks whether two variables point to the exact same object in memory:

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

print(a is b)  # False — they are different objects
print(id(a), id(b))  # Different memory addresses

c = a
print(a is c)  # True — c points to the same object

Caching of small integers:

Python caches integers from -5 to 256, so:

x = 100
y = 100
print(x is y)  # True — cached object

x = 1000
y = 1000
print(x is y)  # False — different objects

Rules of usage:

• Use is only for comparison against None:

# Correct
if value is None:
    print("No value")

# Incorrect
if value == None:
    print("No value")

• When comparing values, always use ==.
• is only checks the id() of the objects — this is useful mostly for singletons like None, True, or False.