What is the use of the "is" keyword in Python?

Question

Jayant Kumar · Accepted Answer

Table of Contants
Introduction
The is keyword in Python is used to check whether two variables point to the same object in memory, making it a comparison of object identity. This differs from the == operator, which compares whether two objects have the same value. By using is, you can determine if two variables reference the exact same object.

How the is Keyword Works
The is operator compares two variables to see if they refer to the same memory location. If they do, is returns True; otherwise, it returns False.
Syntax:
a is b

This checks if a and b point to the same object.
Example:
a = [1, 2, 3]
b = a
c = [1, 2, 3]

print(a is b)  # Output: True (both a and b reference the same list)
print(a is c)  # Output: False (a and c have the same content but are different objects)

In the example, a is b returns True because both variables refer to the same object in memory, while a is c returns False because c is a different list object, even though its contents are identical.

Difference Between is and ==

**is**: Compares the identity of two objects (whether they are the same object in memory).
**==**: Compares the values of two objects (whether their contents are the same).

Example:
x = [1, 2, 3]
y = [1, 2, 3]
z = x

print(x == y)  # Output: True (x and y have the same contents)
print(x is y)  # Output: False (x and y are different objects)
print(x is z)  # Output: True (x and z refer to the same object)

In this case, x == y evaluates to True because the contents of the lists are the same, but x is y evaluates to False because they are two distinct objects in memory. Meanwhile, x is z is True because z refers to the same list as x.

Use Cases for the is Keyword
1. Checking for Singleton Objects (e.g., **None**)
One of the most common uses of the is keyword is to check if a variable is None, as None is a singleton in Python (there is only one instance of it in memory).
Example:
a = None

if a is None:
    print("a is None")  # Output: a is None

This ensures that you're comparing the memory location of a with the singleton None, which is the correct way to check for None in Python.
2. Comparing Immutable Objects (e.g., Integers, Strings)
Python often reuses memory for small integers and strings to save space, so comparing these objects with is might return True even though they are separate variables.
Example:
a = 10
b = 10

print(a is b)  # Output: True (Python reuses memory for small integers)

x = 1000
y = 1000

print(x is y)  # Output: False (different memory locations for larger integers)

This optimization is called "interning" and applies to certain immutable types like small integers and short strings.

Conclusion
The is keyword in Python is used to compare the identity of two objects, checking if they occupy the same memory location. It's especially useful when working with singleton objects like None or when you need to verify that two variables point to the same object. While is checks object identity, the == operator checks value equality, making it essential to choose the right operator depending on your specific use case.

What is the use of the "is" keyword in Python?

Table of Contants

Introduction

How the `is` Keyword Works

Syntax:

Example:

Difference Between `is` and `==`

Example:

Use Cases for the `is` Keyword

1. Checking for Singleton Objects (e.g., `None`)

2. Comparing Immutable Objects (e.g., Integers, Strings)

Conclusion

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