LIST COMPREHENSION.

What is list comprehension?

List comprehension is an elegant way to create lists. A python list comprehension consists of expressions enclosed by square brackets.

For example:

#Normal way to create list.
x=[]
for i in range (11):#creating a list from 0 to 10 
    x.append(i)
print(x)

output:-  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

#List comprehension.
x=[i for i in range(11)] #creating a list from 0 to 10
print(x)

output:-  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Advantages of list comprehension over normal way.

1. More time efficient and space efficient than loops.

2. Requires fewer lines of code.

Working of list comprehension.

x=[(expression to get displayed ) (for loop , for range of elements) (conditions)]

For example:-

x=[i for i in range(1,11) if i%2==0]
#expression followed by range and condition
print(x)

output:-[2, 4, 6, 8, 10]

Some examples of comprehension.

1. Creating a list of even numbers from 0 to 100.

x=[i for i in range(100) if i%2==0 ] 
#range of 100 numbers with condition.
print(x)

output:-[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98]

2. Nested list comprehension.

#This is called matrix and a nested comprehension.
x=[[i for i in range(3)] for j in range(5)]
#range from 1 to 3 and number of repetitions 5
print(x)

output:-[[0, 1, 2], [0, 1, 2], [0, 1, 2], [0, 1, 2], [0, 1, 2]]

3. Squares of 10 numbers.

x=[i**2 for i in range(1,11)]
print(x)

output:-[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]