At first glance, == and Is might seem interchangeable in Python, but they do very different things. If you’ve ever compared two variables and got surprising results, chances are you mixed up equality and identity. Here’s what’s really going on.

Understanding the Difference between == and Is

You may encounter confusing behavior in Python when comparing two objects using == and Is. For example:

a = [1, 2, 3]
b = [1, 2, 3]
print(a == b) # True
print(a is b) # False

Or even more surprising:

x = 256
y = 256
print(x is y) # True
x = 257
y = 257
print(x is y) # False

So what’s going on here? Aren’t both values the same?

Understanding the Difference between == and Is

This confusion arises because == and Is perform different kinds of comparisons in Python:

  • == checks for value equality – whether the values of two objects are the same.
  • Is checks for identity – whether two references point to the same object in memory.

Here’s the difference in simple terms:

  • a == b → Do they look the same?
  • a is b → Are they literally the same object?

Interning in Python (The 256 Example)

Python internally caches small integers and some strings for performance. For example, all integers between -5 and 256 are singleton objects, meaning x = 256; y = 256 will point to the same object. But beyond that, Python may create separate objects even if the values are the same.

So:

x = 256
y = 256
x is y # True (cached)

But:

x = 257
y = 257
x is y # False (not cached)

This is an implementation detail, not something to rely on in your code.

Steps to Resolve the Issue

Step 1: Use == When Comparing Values

If you want to know whether two variables represent the same value, always use ==:

if user_input == expected_value: print("Match found")

This applies to strings, lists, numbers, and even custom objects (if they implement __eq__).

Step 2: Use is Only When Checking Identity

Use is only when you want to check if two variables point to the same object for example, checking for None:

if variable is None: print("No value provided")

This is safe because there’s only one None object in Python.

Step 3: Avoid is for Comparing Immutable Values

Avoid writing:

if x is 1000: ...

Instead, write:

if x == 1000: ...

Because Python may or may not reuse objects depending on the interpreter, version, or optimization level.

Quick Recap

The == operator compares the values of two objects, while is compares their identities (memory addresses). Many subtle bugs can occur if you use is where == is intended — especially when dealing with numbers, strings, or other immutable types.

Best Practices:

  • Use == for value comparison
    Use is for identity checks (None, singleton patterns, etc.)
  • Don’t rely on Python’s internal interning behavior for optimization logic

Conclusion

Knowing the difference between equality and identity in Python can make your code easier to understand and less error-prone. In bigger projects or when reviewing other people’s code, small mistakes around this can lead to tricky bugs. If you want to catch these issues early and build more reliable systems, it can be really helpful to hire Python developers who know how to handle this well.