What is List Comprehension in Python

What is List Comprehension in Python and its Advantages?

The use of computers has evolved over the centuries. They were primarily invented to carry out complex mathematical operations. However, in the last few decades, computers have been used for many advanced purposes, such as artificial intelligence, data analysis, and machine learning. The significant change in computer operations made it necessary to optimize computer memory. It gave birth to the concept of lists in programming languages that allow for the manipulation of symbols and do not restrict the computer’s memory to specific variables. That also created the need for list comprehension, which provides a simple way to create these lists. For anyone interested in coding, it is important to have a clear understanding of the meaning of lists. Let us find out what is list comprehension in Python, its advantages, and its uses.

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What is List Comprehension in Python?

To begin with, one should be familiar with the meaning of both the terms, list, and comprehension. 

Lists, also called arrays, are data types in programming languages. The classification or arrangement of data into different categories based on their characteristics are called data types. The most common examples of data types in Python include integers, strings, characters, int, floats, and Boolean. Lists are built-in versatile data types in Python that store a specific data category. 

They store multiple items in a single variable and follow an index from 0 to 1 to number all the items. The first item in a list is marked 0, the second is marked 1, and so on. Moreover, the items in a list are arranged in a particular order. It means you cannot add an item in between. The new items automatically go to the end of the list. You can create a new list using Python’s list() constructor.

However, when you want to create a new list based on an existing list, you need to use comprehension in Python. It helps generate a concise code by creating new sequences from the existing sequences. This is one of the biggest advantages of using Python. It allows you to write clear, easy-to-read code. 

There are four types of comprehension in Python for different data types – list comprehension, dictionary comprehension, set comprehension, and generator comprehension.

Here, we’re talking about what is list comprehension in Python. Simply put, it is a function that allows you to create a new list from an existing list without writing elaborate code. You can use Python’s list comprehension to generate any existing list output. Let us look at an example.

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Consider a List of Even Numbers

L1 (2, 4, 6, 8, 10).

Now, if you want the square of all numbers present in list 1, you can use list comprehension.

Here is how you can do it.

square = [item**2 for items in L1]

print (square)

Output = [4, 16, 36, 64, 100]

Important Elements of List Comprehension

  • There is an input sequence or the existing list from which a new list is prepared.
  • A variable represents the items contained in an input sequence.
  • You can also add a condition to create a new list from the existing list by using a predicate function.
  • Output is generated from the input sequence by satisfying the predicate expression.

The syntax of list comprehension in Python consists of square brackets followed by a ‘for’ or ‘if’ clause called predicate expression. Here are some examples to help you better understand what is list comprehension in Python:

Example 1: Creating a new list using for

list1 = [8, 9, 10, 11]

new_cube_list = [item**3 for item in list 1]

print (new_cube_list)

Output = [512, 729, 1000, 1331]

Example 2: Creating a list of the first alphabet of every word in an existing list.

list1 = (‘red’, ‘green’, ‘blue’, ‘yellow’, ‘black’, ‘pink’)

new_word_list = [ word[0] for word in list1]

print (new_word_list)

Output = [‘r’, ‘g’, ‘b’, ‘y’, ‘b’, ‘p’]

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Benefits of List ComprehensionProfessional Certificate in Coding: Full Time Coding Bootcamp at MIT xPRO

List comprehension is one of the most remarkable features of Python that enables writing clear and concise codes. Some of its significant benefits are:

  • Facilitates writing the code in fewer lines
  • Allows writing codes that are easier to understand and that adhere to Python guidelines
  • Converts iterable (list) into a formula
  • Filters and maps the items in a list to boost code performance

When to Use List Comprehension

You can use list comprehension in Python to repeat a code multiple times or to modify or filter the items in a list. Therefore, you can use list comprehension as an alternative to loop or lambda in Python to transform items in an existing list.

Tips on Using List Comprehension

Using list comprehension in Python is a difficult task, especially for beginners. These tips on using list comprehension in Python will

Use Conditional Logic

If-else statements, also called conditional statements in programming, add logic to a code that can be executed only when certain conditions are met. Using conditional logic in list comprehension gives you more accurate results and allows you to modify a list or filter unnecessary items.

Use Set and Dictionary Comprehension

Dictionary in Python is a data type that stores data in the form of key-value pairs. For instance, apple:red, and mango:yellow. Here, apple and mango are the keys, and red and yellow are the values. Set is a data type that comprises elements in an abstract manner and has no duplicate items. You can use set and dictionary comprehension to modify list comprehensions.

Use the Walrus Operator

The Walrus operator is an expression that assigns value to a variable in Python. You can use the Walrus operator with list comprehension to avoid calling the same function numerous times.

When to Not Use List Comprehension

Even though list comprehension can make writing codes easier, you do not have to use it every time. You should not use list comprehension in the following circumstances.

Elaborate Code

When your code is too elaborate or complex, it is better to avoid list comprehension as it can be difficult to understand the code and hamper its performance. You can consider using a loop or other functions if the list comprehension expression is too lengthy.

No Use of Existing List

The whole purpose of using list comprehension in Python is to generate a new list that is related to or dependent on an existing list. However, if you don’t have to modify an existing list, you should not use list comprehension.

Writing Matrix

You should not use list comprehension when you are writing a matrix because it flattens the code and makes it difficult to understand.

The majority of programming languages have the same basic structure. If you want to be a programmer or build a career in the IT sector, it is essential to learn basic concepts like what is list comprehension in Python. It is one of the most popular questions in software developer interviews. Emeritus’ online courses on coding will help you learn the fundamentals of programming and offer practical training to boost your career in the IT sector.

By Sneha Chugh

Write to us at content@emeritus.org 

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