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List Comprehension in Python

It provides a short syntax to create new lists. Normally, we create lists like this -


list1=[]
for i in range(1,6):
list1.append(i)

print(list1)

Output

[1, 2, 3, 4, 5]

Using List Comprehension, we can create new lists in just 1 line of code.


list2=[i for i in range(1,6)]
print(list2)

Output

[1, 2, 3, 4, 5]

A variety of lists can be created in this way.


m=[1 for i in range(1,6)]
print(list3)

print()

n=[i for i in "Rapid"]
print(list4)

Output

[1, 1, 1, 1, 1]

['R', 'a', 'p', 'i', 'd']

We can also use if-else statements in list Comprehension.


list5=[i for i in range(1,10) if i%3==0 ]
print(list5)

print()

mylist=["Rapid", "Coders", "Excellent", "Coders"]

list6=[i if i != "Excellent" else "Good" for i in mylist ]

print(list6)

Output

[3, 6, 9]

['Rapid', 'Coders', 'Good', 'Coders']

Nested List Comprehension

Suppose that you want to create a nested list with numbers from 1 to 5 in every list. In one line, you can do it like this -


list7=[[i for i in range(1,6)] for j in range(1,6)]
print(list7)

Output

[[1, 2, 3, 4, 5], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5], [1, 2, 3, 4, 5]]

Now, suppose you want to flatten the above list. You can do it like -


list8=[i for j in list7 for i in j]
print(list8)

Output

[1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5]

Suppose you want to get the tables of all numbers from 2 to 5. You can do it like -


tables=[[i*j for i in range(1,11)] for j in range(2,6)]

for table in tables:
    print(table)

Output

[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
[3, 6, 9, 12, 15, 18, 21, 24, 27, 30]
[4, 8, 12, 16, 20, 24, 28, 32, 36, 40]
[5, 10, 15, 20, 25, 30, 35, 40, 45, 50]

Advantages of List Comprehension

It is easy to use.
Reduces lines of code.
Easy to understand.

Please note that every list cannot be created using List Comprehension.