Python List Comprehension

List comprehension is nothing but writing the logic on the python lists in a brief or short way.
Lets start with an example,

# Here is the code snippet to find the square of each item in the list
# Append to the new list

l_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
new_list = []

for each_item in l_list:
    new_list.append(each_item ** 2)

print(new_list)

List comprehension for the above code will be,

l_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
new_list = [each_item ** 2 for each_item in l_list]

print(new_list)



# Using Python list comprehension the no of lines of code is reduced from 3 to 1. 

Explanation for the above code,

In the above picture,

• Step1 represents the new list creation
• Step2 represents placing the for loop in to comprehensive way
• Step3 represents placing the square of the each item into the list

Lets see another example, finding the positive numbers in a given list.

# Here is the code snippet to find the squares of numbers in the list
# Append to the new list

l_list = [[1, 2, 3],
          [-1, 0, 1],
          [2, -4, 2]]
new_list = []

for sub_list in l_list:
    temp = []
    for item in sub_list:
        if item > 0:
            temp.append(item)
    new_list.append(temp)

print(new_list)

List comprehension for the above code is,

l_list = [[1, 2, 3],
          [-1, 0, 1],
          [2, -4, 2]]
new_list = [[item for item in sub_list if item > 0] for sub_list in l_list]

print(new_list)

How we did it,

In the above example, it is clearly shown how two for loops are merged into a single line using Python list comprehension.

Some points on Python list comprehension:

• Concise and shorter code
• Python list comprehension can used
  
  • To make a new list where each element is the result after a certain operation
  • To make a sub list after checking some condition on each item of the list
• All the logics on list can not be comprehended
• Python list comprehensions are not readable or understandable for beginners
• Its your choice to use Python list comprehension or not. Not mandatory to use.

Hope you got some idea on writing list comprehensions. Thanks for reading. Happy learning. Please comment if you dont understand any point in here or if you find any thing wrong. Thankyou.