“Is” Operator Behaves Unexpectedly With Integers

So you happen to find that the “is” operator at many instances behaves unexpectedly with integers. You might have used the “is” operator instead of “==”, thinking that they are but the same! Did you?

Sometimes programmers get confused with “is” and “==” operators available in Python. Not knowing which one to use, they tend to use both is & == interchangeably without bothering about the result. 

Why does the is operator behaves unexpectedly with integers?

A beginner might not know that is and == operators are two different Python operators. Yes! Though Python users might have faced the problem during the comparison of numbers (or variables). The most common problem is that the “is” operator behaves unexpectedly with integers. This issue seems as:

x = 123y = 123x is y
True
x = 257y = 257x is y
False

Note: The current code has an array of integer objects that lies between -5 to 256. In case, the integer value is greater than 256, it will return the false value. But we have solved this issue in this blog. Scroll down to check the solution.


257 is 257

True

Why this result?

So, what actually is happening here? And why “is” operator still useful? When to use the “is” operator? We have explained all the answers to such questions that might be hitting your brain. Moving further with more related concepts in Python.  

Attention:

Read this blog carefully as at the end of the blog, I have given some of the Multiple Choice Questions. These questions are based on what you have read and learned from this blog. 

Therefore, it is advised to answer all the questions so that you can easily check your knowledge. We have written the blog such that you would probably be able to answer all the below questions after a good read.

First, let’s understand what is happening in the above program!

In the above program, the is operator is not testing the object identity. That is why it returns true when and only when the x and y belong to the same objects. 

To test the object identity, use the id which is the “identity.” It guarantees to be constant and unique for the particular object during its lifetime. 

Note that the two objects can have a similar id() value. And use it as:

id(x )== id(y)

Isn’t the “is” operator similar to the “==” operator?

No, not at all!!

Both operators have a difference among their functionalities. Like “is” operator is an identity operator. On the other hand, the == operator is an equality operator that compares the values of the operators and checks value equality. 

Let’s understand with examples

Output

Correct

Output

Incorrect

Output

Correct

Output

incorrect 

So, what is executed in the above code?

  • The first if condition gives the output as “correct” because both x and y are empty lists.
  • In the second, if condition, the output is “incorrect” as both empty lists have distinct memory locations. That is why x and y refer to dissimilar objects. [NOTE: You can check the identity of both objects using the id function. How? The example is given below.]
  • The third “if” condition gives the output as “correct” because both x and z point to a similar object.
  • Again, the fourth “if” condition is “incorrect” as the sequence of both lists gives a new list.
Key point:
How to use the id function?
x= [ ]y= [ ] print(id(x))print(id(y))

Output:
140619854361808140619854362240

This represents that x and y refer to separate objects.

Why is the “is” operator still useful?

Python users use the is operator when they need to compare a number or variable. Moreover, you might have heard that is operator is much faster than the == operator. 

Although there is a notable difference between both operators. This is the common reason why is operator still in use.

Apart from this, is operator is the identity operator, which is used for checking whether two numbers or variables belong to the same object in the memory or not. 

It compares the identities of two objects. The output of the code will return TRUE when the operands refer to a similar object (or are identical).

When should I use the “is” and “==” operator?

There are two rules to use “is” and “=” operator, and these are:

  1. Use the “==” operator in the case when your main goal is to compare the values/content of the two objects. And the location of objects does not matter for you.

On the other hand, use the “is” operator when there is a need to check whether the variables are pointing to a similar memory location/address or not.

lst1 = [1, 2]lst2 = [3, 4]lst3 = [1, 2]lst3=lst1 if (lst1 is lst3):        print(“Right”)
else:        print(“Wrong”)
print(id(lst1))print(id(lst2))print(id(lst3))




Output:
Right140057189496016140057189496448140057189496016

Note: You can see that lst1 and lst3 are pointing to a similar memory location/address.

  1. Python users should use the “==” operator when they need to perform string comparison. Python has the capability to compare character by character.

Let’s take an example to understand: is operator behaves unexpectedly with integers

lst1 = [1, 2, 0]lst2 = [1, 2, 0]lst3 = [1, 2, 3]
 if (lst1 == lst3):        print(“Right”)

else:        print(“Wrong”)
if (lst1 == lst2):        print(“Right”)

else:        print(“Wrong”)






Output:

WrongRight

You can see that lst1 and lst3 have three elements in the list. And two are the same but the third one is not. That is why the first condition output is Wrong. On the other hand, lst1 and lst2 have the same elements with value values; therefore, the second condition output is Right.

Attention:

Doesn’t the “is” operator take much time to compare the elements?

No, not at all!! Rather than comparing all content, the “is” operator can compare the memory location. Therefore, it works much faster and there is also less CPU utilization.

Finally, we can conclude that we should use the “is” operator instead of the “==” operator to speed up the heavy or large string comparison operations.

Bonus Point:
Python users can use the “is not ” or “!=” operator to compare the objects. The output of the program with the “is not” operator is true when two operands are not equal. Otherwise, the Python program with the “is not” operand shows the output as false.

Conclusion

So, now that you agree, is operator behaves unexpectedly with integers, avoid this confusion.

Everything in Python considers to be an object and each object possesses a particular memory location. Therefore, Python users can use “is” and “is not” operators to check if the two variables have similar memory locations or not. 

Use “id” (refers to identity) that guarantees to be constant and unique for the particular object(s) during the lifetime. Above, I have solved the issue related to the “is” operator. Moreover, I have differentiated the use of the “is” and “==” operators. 

We hope, we could successfully solve your query related to the “is” operator. In case, you still have any queries, comment in the below “comment section.” I will do my best to solve the query in the best possible way. 

“Keep practicing the Python programs to become the master of it”

Take a test to check what you have studied 

  1. Which of the following operators is used to check whether two objects have similar memory locations or not?

(A) in operator

(B) is operator

(C) ==

(D) **

Correct Answer: (B) Is operator is used for checking the memory location of the objects.
  1. Which of the following operators is used to compare two operands’ equality?

(A) == operator

(B) is operator

(C) is not operator

(D) != operator

Correct Answer: (A) “==” operator is used to check whether two operands have equality or not.

Test your “operator in python” skills!

  1. Do I need to use the == operator to determine if the objects of float types are equal or not?

(A) No, it is not necessary

(B) Yes, it is necessary

Correct Answer: (A) The internal representation of float objects is not mandatory.
  1. For two objects a and b:

a is b is True, if and only if

id(a)==id(b)

(A) True

(B) False

Correct Answer: (A) It is true because a and b objects can be equal if their identity is also equal.
  1. If two operands are not equal and the condition is true, then which operator will be used?

(A) ≠

(B) ==

(C) is

(D) !=

Correct Answer: (D) “!=” operator is used when the two values of two operands are not equal, and the condition is true.

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Have a query? Feel free to drop it in the comments below. You may drop your contact as well, our Experts will surely get back to you for any further doubts. Do it here!

Keep Learning. As tech deserves you!

Archana

A traveler, and explorer, Archana is an active writer at GUVI. You can usually find her with a book/kindle binge-reading (with an affinity to the mystery/humor).

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