What is List Comprehensive in Python

What is List Comprehensive in Python

List comprehension is a concise and efficient way to create and manipulate lists in Python. It allows you to generate new lists by applying an expression to each item in an existing iterable (like a list, tuple, string, or range) and optionally filtering the items based on a condition.

[expression for item in iterable if condition]


expression: The expression that is evaluated for each item in the iterable and added to the new list.
item: The variable representing each element in the iterable.
iterable: The collection (like a list, range, string, etc.) that you are looping over.
condition (optional): A conditional expression to filter which items should be included in the new list.
        

Below are different range of examples.

# To Print All Even Numbers
L = [i for i in range(1,11)]
[i for i in range(1,11) if i%2 ==0]


Output : [2, 4, 6, 8, 10]
        

# Scalar multiplication on a vector
v = [2,3,4]
s = -3
[s*i for i in v]


Output : [[-6, -9, -12]]
        

# Print all numbers divisible by 5 in the range of 1 to 50
[i for i in range(1,51) if i%5 == 0]

Output : [5, 10, 15, 20, 25, 30, 35, 40, 45, 50]
        

# Nested if with List Comprehension
# add new list from my_fruits and items if the fruit exists in basket and also starts with 'a'

basket = ['apple','guava','cherry','banana']
my_fruits = ['apple','kiwi','grapes','banana']

[i for i in my_fruits if i in basket and i.startswith('a')]

Output : ['apple']
        

# Print a (3,3) matrix using list comprehension -> Nested List comprehension
[[i*j for i in range(1,4)] for j in range(1,4)]

Output : [[1, 2, 3], [2, 4, 6], [3, 6, 9]]
        

# cartesian products -> List comprehension on 2 lists together
L1 = [1,2,3,4]
L2 = [5,6,7,8]

[i*j for i in L1 for j in L2]

Output : [5, 6, 7, 8, 10, 12, 14, 16, 15, 18, 21, 24, 20, 24, 28, 32]
        

# Remove vowels from a string
words = ['apple', 'banana', 'cherry']

[''.join([i for i in j if i not in ('a','e','i','o','u')]) for j in words]

Output : ['ppl', 'bnn', 'chrry']
        

# Multiply elements of two lists element-wise

list1 = [1, 2, 3]
list2 = [4, 5, 6]

[list1[i]*list2[j] for i in range(0,len(list1)) for j in range(0,len(list2)) if i==j]

Output : [4, 10, 18]
        

# Extract digits from a string

words = ['abc123', 'test456', 'hello', '789']

[''.join([i for i in j if i.isnumeric()])for j in words]

Output : ['123', '456', '', '789']     
        

# Write a list comprehension that can transpose a given matrix
matrix = [[1,2,3],[4,5,6],[7,8,9]]

[[m[i][j] for i in range(0,len(m))] for j in range(0,len(m))]

Output : [[m[i][j] for i in range(0,len(m))] for j in range(0,len(m))]
        

# Write a list comprehension to print the following matrix [[0, 1, 2], [3, 4, 5], [6, 7, 8]]
[[i*3+j for j in range(3)] for i in range(3)]

Output : [[0, 1, 2], [3, 4, 5], [6, 7, 8]]
        

# Convert Character Matrix to single String using string comprehension.
Input: [['c', 'a', 'm', 'p', 'u', 'x'], ['i', 's'], ['b', 'e', 's', 't'], ['c', 'h', 'a', 'n', 'n', 'e', 'l']]

' '.join([''.join(i) for i in L])

Output: campux is best channel    
        

Advantages of List Comprehension:

1.) Concise: It's shorter than using traditional for loops, making your code cleaner and easier to understand.
2.) Faster Execution: In many cases, list comprehensions are faster than equivalent for loops because they are optimized internally by Python.
3.) Readability: It reduces the need for more complex loops, which improves the readability of your code.

In summary, list comprehension is a powerful feature in Python that allows you to create and manipulate lists more efficiently and concisely, making your code both cleaner and faster.

Happy Learning!!!! 😀