List & Dictionary Comprehension in Python

List Comprehension

Python lists are a fundamental data structure for storing and managing data collections. Lists are adaptable, flexible, and may store a variety of data kinds, including integers, strings, and even other lists. List comprehension lets you make a new list by applying an expression to each item in an existing iterable (such as a list, tuple, or range) and optionally filtering the items depending on a condition. List comprehensions are a more compact and readable means of creating lists than typical for loops. As an example, suppose we want to create a new list of even numbers from a list of random numbers.

numbers = [84, 77, 50, 89, 33, 36, 59, 31, 76, 1, 20, 58, 59, 93, 70, 28, 51, 7, 48, 74]

Using a for loop

even_numbers = []

for number in numbers:
    if number % 2 == 0:
        even_numbers.append(number)

Using list comprehension

even_numbers = [num for num in numbers if num % 2 == 0]

the syntax for list comprehension is :

list = [new_item for item in some_list if conditional_statement]

Dictionary Comprehension

Dictionaries in Python are a versatile data structure that may be used to store and manage collections of key-value pairs. Dictionary comprehension is a simple and effective method for creating dictionaries in Python. You can create dictionaries by specifying key-value pairs based on an expression and an iterable. Dictionary comprehensions are a logical extension of list comprehensions and a useful feature for easily generating dictionaries without the use of explicit loops.

suppose we have a dictionary of cars and year of manufacture, and we want to create a dictionary of recently manufactured ones

car_dictionary = {
    "Tesla Model 3": 2020,
    "Toyota Camry": 2022,
    "Ford Mustang": 2021,
    "Honda Civic": 2023,
    "Chevrolet Silverado": 2019
}

using a for loop

recently_manufactured = {}

for (car,year) in car_dictionary.items():
    if year > 2021:
        recently_manufactured[car] = year

using dictionary comprehension

recently_manufactured = {car:year for (car, year) in car_dictionary.items() if year > 2021}

the syntax for dictionary comprehension is:

dictionary = [new_key:new_value for (key, value) in some_dict.items() if conditional_statement]