Python

Python List Comprehension

April 3, 2025 No comments yet

Example 1

Add Integers

number_list = [10, 20, 30]
number_plus_5 = [x + 5 for x in number_list] print(number_plus_5)

[15, 25, 35]

What would this look like as a for loop?

for_number_plus_5 = []
for x in number_list: for_number_plus_5.append(x + 5) print(number_plus_5)

[15, 25, 35]

Example 2

Integer Multiplication

number_mul_3 = [x * 3 for x in [8, 11, 17]] print(number_mul_3)

[24, 33, 51]

Example 3

String

teams = ['Rays', 'Yankees', 'Red Sox', 'Blue Jays', 'Orioles']
uppercase_teams = [x.upper() for x in teams] print(uppercase_teams)

[‘RAYS’, ‘YANKEES’, ‘RED SOX’, ‘BLUE JAYS’, ‘ORIOELS’]

Example 4

String Length

team_length = [len(team) for team in teams] print(team_length)

[4, 7, 7, 9, 7]

Example 5

Characters in a string

enter_sandman = [character for character in "We're off to never-never land"] print(enter_sandman)

[‘W’, ‘e’, “‘”, ‘r’, ‘e’, ‘ ‘, ‘o’, ‘f’, ‘f’, ‘ ‘, ‘t’, ‘o’, ‘ ‘, ‘n’, ‘e’, ‘v’, ‘e’, ‘r’, ‘-‘, ‘n’, ‘e’, ‘v’, ‘e’, ‘r’, ‘ ‘, ‘l’, ‘a’, ‘n’, ‘d’]

Example 6

Another Characters in a string

metallica_songs = ['Orion', 'Nothing Else Matters', 'Eye of the Beholder']
first_char = [song[0] for song in metallica_songs] print(first_char)

[‘O’, ‘N’, ‘E’]

Example 7

if else only to the left of the for loop

if only to the right
bands = ['Metallica', 'NIN', 'A Perfect Circle', 'Northlane']
new_bands = [x if x != "NIN" else "Nine Inch Nails" for x in bands] print(new_bands)

[‘Metallica’, ‘Nine Inch Nails’, ‘A Perfect Circle’, ‘Northlane’]

Example 8

single if with numbers
concert_db = [80, 110, 60, 70, 120]
loud_concerts = [db for db in concert_db if db > 60] print(loud_concerts)

[80, 110, 70, 120]

Example 9

single if with chars

enter_sandman_vowels = [character for character in "We're off to never-never land" if character in "aeiou"] print(enter_sandman_vowels)

To start we’re going to create a simple dataframe in python:

Example 10

Multiple If

numbers = [2, 5, 8, 9, 12, 15, 18, 20, 24]
even_and_divisible_by_3 = [x for x in numbers if x % 2 == 0 if x % 3 == 0] print(even_and_divisible_by_3)

Example 11

Range

numbers_squared = [x ** 2 for x in range(10)] print(numbers_squared)

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

Example 12

Function with list comprehension

Same as first example
number_list = [10, 20, 30]
def plusfive(num): return num + 5
number_plus_5_v2 = [plusfive(x) for x in number_list] print(number_plus_5_v2)

[15, 25, 35]

Example 13

Multiple List Comparrison
Bands1 = ['Erra', 'Parkway Drive', 'Beartooth', 'In Flames', 'Insomnium']
Bands2 = ['In Flames', 'Dark Tranquility', 'Insomnium', 'Omnium Gatherum', 'Parkway Drive']
matching_bands = [i for i in Bands1 if i in Bands2] print(matching_bands)

[‘Parkway Drive’, ‘In Flames’, ‘Insomnium’]

Example 14

Nested List Comprehensions (Create Matrix)
matrix = [[j for j in range(3)] for i in range(5)] print(matrix)

[[0, 1, 2], [0, 1, 2], [0, 1, 2], [0, 1, 2], [0, 1, 2]]

Example 15

Nested List Comprehensions (Flatten Matrix)
flat_matrix = [i for j in matrix for i in j] print(flat_matrix)

[0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2]

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