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Python Identity Operators

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Description

Identity operators are used to compare the memory locations of two objects—not just their values. These operators help determine if two variables reference the same object in memory.
Python provides two identity operators:
Operator Description Example Result
is Returns True if both refer to the same object x is y True/False
is not Returns True if they refer to different objects x is not y True/False

Prerequisites

  • Understanding of variables and memory references.
  • Familiarity with mutable vs immutable data types.
  • Knowledge of objects vs values.

Examples

Here's a simple program in Python:

# Simple identity check with integers
a = 10
b = 10
print(a is b)        # True (small integers are cached in memory)

# Identity with lists (mutable)
x = [1, 2, 3]
y = [1, 2, 3]
print(x == y)        # True (values are equal)
print(x is y)        # False (different objects)

# Assign same reference
z = x
print(z is x)        # True (same object)

# Using 'is not'
print(x is not y)    # True

Real-World Applications

Caching systems: Check if objects are reused or recreated.

Memory management: Ensure two variables don’t point to the same object when not intended.

Singleton design pattern: Confirm only one instance exists.

Object pooling: Check object identity before reusing.

Frameworks: Many ORMs and libraries internally use identity checks for optimization.

Where topic Can Be Applied

Object comparison: For references, not content.

Debugging tools: To inspect if multiple variables refer to the same object.

Immutable vs mutable design: Ensures copy vs reference behavior.

Machine learning models: Manage large model weights or config objects by reference.

State management: In UI frameworks or reactive programming.

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Interview Questions

What is the difference between == and is?

When does a is b return True even if they were declared separately?

Can two different lists be is equal?

How does Python handle memory for small integers and strings?

What will be the result of: a = "hello"
b = "hello"
print(a is b)