What is the difference between is and == in Python?

In Python, is and == look similar but they check completely different things. == checks for value equality, meaning it compares whether the values of two objects are the same. But is checks for identity, meaning it verifies whether both variables point to the exact same object in memory.

For example:

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

print(a == b)   # True → same value
print(a is b)   # False → different memory objects

Even though the lists look identical, they’re stored separately in memory, so is is false.

I applied this concept while working on object comparisons in a configuration system. We had to compare config values, not objects themselves, so using == was correct. But there was one case where we needed to verify if two variables were referencing the same instance of a cached object; there, is helped ensure we weren’t accidentally creating duplicates.

A challenge I faced was with small integers and strings. Python internally reuses (“interns”) some immutable values. So sometimes:

x = 10
y = 10
print(x is y)  # True

This can mislead beginners into thinking is checks values. I once saw a bug where a teammate used is instead of == for string comparison. It worked in testing but failed in production because the strings were created differently and had different memory references. We fixed it by replacing all identity checks with == when comparing values.

A limitation of is is that it’s only meaningful when checking identity, such as None comparisons:

if value is None:
    ...

Using == None can be overridden by custom __eq__ logic, so is is the safest here.

An alternative, when comparing values or structures, is always to use ==. Identity checks should be used only when you explicitly want to verify the same object.

So in practice:

• Use == when checking if values match.
• Use is only when checking if two variables reference the same object, especially for singletons like None.