List comprehensions provide a concise and readable way to create new lists, sets, or dictionaries by iterating over sequences (like lists, strings, or ranges) and optionally applying transformations or conditions.

List comprehensions

List comprehensions allow building new lists from existing iterables with optional transformations and filtering.

list1 = [letter for letter in "abcd"] # dividing a string into a list of characters
print(list1)

list2 = [int(character) for character in "0123456"] # converting each character in a string to an integer
print(list2)

x, y, z = [int(x) for x in input("Enter three numbers separated by spaces: ").split()] # using split() with a list comprehension to get three input values in one line
print(x + y + z)

list3 = [["a", "b"] for x in range(10)] # creating a two-dimensional list
print(list3)

list4 = [x.lower() for x in "ABCDE"] # converting every character in a string to lowercase
print(list4)

l = [{"name": "x", "value": 1}, {"name": "y", "value": 2}]
list5 = [x["name"] for x in l] # extracting the "name" value from each dictionary
print(list5)

list6 = [x * y for x, y in ([1, 2], [3, 4])] # multiplying elements of two lists element-wise (x from first list, y from second list) - 1*3, 2*4
print(list6)

text = "one: 1, two: 2, three: 3, four: 4"
list7 = [int(character) for character in text if character.isdigit()] # extracting numbers from a string
print(list7)
                                

squares = [x * x for x in range(5)] # creating a list of squares of numbers from 0 to 4
print(squares)

div_by_7 = [x for x in range(1, 1001) if x % 7 == 0] # creating a list of numbers divisible by 7 from 1 to 1000
print(div_by_7)

contain_3 = [x for x in range(1, 1001) if "3" in str(x)] # creating a list of numbers from 1 to 1000 containing the digit 3
print(contain_3)

text = "This is an example string"

spaces_count = [1 for char in text if char == " "] # counting spaces in a string
print(sum(spaces_count))

no_vowels = [char for char in text if char.lower() not in "aeiou"] # removing vowels from a string
print("".join(no_vowels))

words = text.split()
short_words = [word for word in words if len(word) < 4] # finding words with less than 4 letters
print(short_words)
                                

Filling a list with zeros

list1 = [0] * 10
list2 = [0 for _ in range(10)]
list3 = list(0 for _ in range(10))
                                

Set comprehensions

set1 = {x * x for x in range(10)} # creating a set of squares of numbers from 0 to 9
print(set1)
                                

Dictionary comprehensions

dict1 = {x: x * x for x in range(10)} # creating a dictionary with numbers as keys and their squares as values
print(dict1)

dict2 = {x: x**3 for x in range(10) if x % 2 == 0} # creating a dictionary with even numbers as keys and their cubes as values
print(dict2)

letters = "abcd"
dict3 = {char: char.upper() for char in letters} # creating a dictionary mapping lowercase letters to uppercase letters
print(dict3)