In Python, What is Returned When Evaluating [n for n in range(10) if n % 2]?

In Python, What is Returned When Evaluating [n for n in range(10) if n % 2]?

The expression [n for n in range(10) if n % 2] is an example of list comprehension. We use a for loop and an if statement together in this expression. If the if conditional holds true, the value of n will be stored in a list.

After evaluating the expression [n for n in range(10) if n % 2], we get the following output:

List comprehension helps us avoid long codes. That is why we got a list of odd integers just by writing one line of code. To learn more about list comprehensions, refer to this article.

Expanding the List Comprehension Into a for Loop

Let us say we have the following list comprehension stored in the variable new_list:

Output:

After using list comprehension, we got a list consisting of odd integers up to 10.

We can expand the above list comprehension expression into a for loop to understand how we got the above output. After expanding the list comprehension into a for loop, the code will be:

Output:

As we can see in the above code, we created an empty list named new_list and created a for loop to iterate over integers from 0 to 9. Then, we wrote a conditional statement. If the conditional holds true, the integer n will be appended to the list new_list.

List comprehensions help us avoid writing all these lines of code. Instead of writing the above 7 lines of code, we could have done all this work in a single line of code.

Explanation Of The Output

Let us now understand how did we get the output [1, 3, 5, 7, 9] for the list comprehension [n for n in range(10) if n % 2]. Following are the steps explaining the working of the program:

1. We declared a variable n.
2. The variable n is in the range(10) inside the for loop. So, the value of n will range from 0 to 9. In other words, n will take the values 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.
3. An if conditional is applied in the for loop. The conditional checks if the value of n is divisible by 2.
4. If n is divisible by 2, the remainder will be 0. Therefore, the conditional will be False since the boolean value of 0 is False. Hence, n will not be appended to the list.
5. If n is not divisible by 2, the remainder will be 1. Therefore, the conditional will be True. Hence, the variable n will get appended to the list.
6. Finally, after the completion of the for loop, we will get a list of odd integers.

Learn More

• Python Comprehensions
• List Methods in Python
• Range Function in Python
• Empty List in Python