How do you rotate an element in python?

The rotation of a list has been discussed earlier also, but this particular article focuses on shorthands and various short techniques to achieve this in one-liners or one word. This operation is quite essential in a programmers life to achieve various tasks.

Let’s discuss different ways we can rotate a list.

Method #1 : Using Slicing
This particular method is the generic method and mostly employed to achieve this task and also been discussed in many articles as well. It works by just joining the later sliced part to the initial sliced part given the rotation number.

test_list = [1, 4, 6, 7, 2]

print ("Original list : " + str(test_list))

test_list = test_list[3:] + test_list[:3]

print ("List after left rotate by 3 : " + str(test_list))

test_list = test_list[-3:] + test_list[:-3]

print ("List after right rotate by 3(back to original) : "

                                         + str(test_list))

Output:

Original list : [1, 4, 6, 7, 2]
List after left rotate by 3 : [7, 2, 1, 4, 6]
List after right rotate by 3 ( back to original) : [1, 4, 6, 7, 2]

 
Method #2 : Using list Comprehension
This problem can also be solved by naive method, but its shorter implementation would be with the help of list comprehension. In this method, we just reassign the index to each value to specific position after rotation.

test_list = [1, 4, 6, 7, 2]

print ("Original list : " + str(test_list))

test_list = [test_list[(i + 3) % len(test_list)]

               for i, x in enumerate(test_list)]

print ("List after left rotate by 3 : " + str(test_list))

test_list = [test_list[(i - 3) % len(test_list)]

               for i, x in enumerate(test_list)]

print ("List after right rotate by 3(back to original) : " 

                                        + str(test_list))

Output:

Original list : [1, 4, 6, 7, 2]
List after left rotate by 3 : [7, 2, 1, 4, 6]
List after right rotate by 3(back to original) : [1, 4, 6, 7, 2]

 
Method #3 : Using collections.deque.rotate()
The collections module has deque class which provides the rotate(), which is inbuilt function to allow rotation. This is lesser known function but has a greater utility.

from collections import deque

test_list = [1, 4, 6, 7, 2]

print ("Original list : " + str(test_list))

test_list = deque(test_list)

test_list.rotate(-3)

test_list = list(test_list)

print ("List after left rotate by 3 : " + str(test_list))

test_list = deque(test_list)

test_list.rotate(3)

test_list = list(test_list)

print ("List after right rotate by 3(back to original) : "

                                        + str(test_list))

Output:

Original list : [1, 4, 6, 7, 2]
List after left rotate by 3 : [7, 2, 1, 4, 6]
List after right rotate by 3(back to original) : [1, 4, 6, 7, 2]

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