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Table of Contents
How == Works – Value Comparison
How is Works – Identity Comparison
When Should You Use Each?
Some Gotchas to Watch For
Home Backend Development Python Tutorial What is the difference between python `is` and `==`?

What is the difference between python `is` and `==`?

Jul 12, 2025 am 02:08 AM
python is and ==

In Python, == compares values while 'is' checks memory identity. 1. == evaluates if two objects have equal values, like a == b for lists with same elements. 2. 'is' determines if two variables reference the exact same object in memory, which is why a is b returns False for separate lists. 3. Use == for value comparisons and 'is' only for checking None or confirming identical object references. 4. Be cautious as small integers and strings may be interned, causing unexpected 'is' results, but this behavior is implementation-dependent and unreliable for general use.

What is the difference between python `is` and `==`?

The difference between is and == in Python is pretty straightforward once you understand what each one actually checks. In short:

What is the difference between python `is` and `==`?
  • == compares the values of two objects.
  • is compares the identities (memory addresses) of two objects.

So even if two variables have the same value, they might not be the same object in memory — which means == could return True while is returns False.


How == Works – Value Comparison

When you use ==, Python checks whether the values of the two operands are equal. This can sometimes involve a lot of behind-the-scenes logic depending on the type of object, especially for custom classes that override equality behavior.

What is the difference between python `is` and `==`?

Examples:

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

print(a == b)  # True – same values

Even though a and b are separate lists, their contents are identical, so == returns True.

What is the difference between python `is` and `==`?

Another example:

x = "hello"
y = "hello"
print(x == y)  # True – both strings have the same characters

This works because immutable types like strings and small integers are often cached or interned by Python, which can affect how is behaves — more on that next.


How is Works – Identity Comparison

The is operator doesn't care about the values — it only checks whether two variables refer to the exact same object in memory.

Using the same list example:

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

print(a is b)  # False – different objects in memory

But if you assign b = a, then they point to the same object:

a = [1, 2, 3]
b = a
print(a is b)  # True – same object

Now any changes made through a will also appear in b, since they reference the same list.


When Should You Use Each?

Use these rules of thumb:

  • Use == when comparing values. That’s almost always what you want.
  • Use is only when checking against None, or when you really need to confirm two names point to the same object.

Examples where is makes sense:

value = None
if value is None:
    print("Value is missing")

Avoid doing this:

x = 5
if x is 5:  # Not reliable!
    print("Yes")

Because for integers and other types, interning may or may not happen — it's implementation-dependent.

Also avoid comparing strings with is:

s = "hello"
if s is "hello":  # Don't rely on this
    pass

Again, string interning varies and shouldn't be trusted unless you're certain.


Some Gotchas to Watch For

Here are a few common surprises people run into:

  • Small integers are interned:

    a = 256
    b = 256
    print(a is b)  # True

    But bigger numbers aren’t:

    a = 257
    b = 257
    print(a is b)  # False
  • Strings with special characters or longer ones may not be interned either.

  • Lists, dicts, and sets are never interned:

    a = {}
    b = {}
    print(a is b)  # False

    These behaviors show why relying on is for general comparisons is risky.


    So yeah, basically == checks if things are alike in value, and is checks if they’re literally the same thing in memory. Most of the time, you’ll stick with ==.

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