Python Identity Operators

Python Identity Operators at a Glance

Every Python value is an object. A variable holds a reference to an object, and identity operators ask whether two references lead to that exact same object.

1. Identity Operators Infographic

Use this visual reference to compare is, is not, object identity, and value equality.

2. Using the IS Operator

Start with two variables containing the same short string:

>>> a = "R1"
>>> b = "R1"
>>> a is b
True

This interpreter reused one string object, so both variables refer to the same identity. That result may look like a value comparison, but it is not.

>>> c = " ".join(["R1", "is", "a", "router"])
>>> d = "R1 is a router"
>>> c == d
True
>>> c is d
False

The strings contain the same characters, but they were created as different objects. Equality is true while identity is false.

3. Inspecting Object Identity with id()

The built-in id() function returns an integer that uniquely identifies an object during its lifetime. Matching IDs prove that two references point to the same object.

>>> a = "R1"
>>> b = a
>>> id(a) == id(b)
True
>>> a is b
True

>>> c = ["R1", "R2"]
>>> d = ["R1", "R2"]
>>> id(c) == id(d)
False
>>> c == d
True

The exact integers returned by id() are runtime-specific, so your output will not match another session's numbers. Compare the results; do not memorize them.

4. Using the IS NOT Operator

The is not operator asks the opposite identity question: do these references point to different objects?

>>> expected = ["R1", "R2"]
>>> discovered = ["R1", "R2"]
>>> expected is not discovered
True
>>> expected != discovered
False

The two lists are different objects, so is not returns True. Their values are equal, so != returns False.

5. Identity vs Equality

Choose the operator from the question you actually need to answer. Identity and equality sometimes produce the same result, but they mean different things.

>>> c = " ".join(["R1", "is", "a", "router"])
>>> d = "R1 is a router"
>>> c == d
True

Use == here because the intent is to compare the text, not the objects that store it.

6. Network Automation Example

Identity operators are appropriate when a function uses None to mean “no result.” This distinguishes a missing response from valid but empty data.

def read_saved_output(hostname):
    saved_outputs = {
        "R1": "show ip interface brief output",
        "R2": ""
    }
    return saved_outputs.get(hostname)

result = read_saved_output("R3")

if result is None:
    print("No saved output exists for R3")
else:
    print(result)

The dictionary method returns the singleton object None when R3 is missing. The check result is None clearly expresses that sentinel test.

7. Common Mistakes and Limits

8. Guided Practice

9. Conclusion

Python's is and is not operators check whether references point to the same object. They do not check whether two values are equal or unequal.

• Use is and is not for identity checks, especially with None.
• Use == and != for strings, numbers, lists, and other value comparisons.
• Use id() for learning and debugging object identity, not as a stored business identifier.
• Do not depend on Python's reuse of short strings or small integers.

I hope you enjoyed this lesson. If you have any questions, please leave a comment.