Python program to Reverse a range in list

Given a List, our task is to write a Python program to reverse a range in the list.

Example:

Input : test_list = [6, 3, 1, 8, 9, 2, 10, 12, 7, 4, 11], str, end = 3, 9

Output : [6, 3, 1, 7, 12, 10, 2, 9, 8, 4, 11]

Explanation : 8, 9, 2, 10, 12, 7 are reversed in list to 7, 12, 10, 2, 9, 8.

Input : test_list = [6, 3, 1, 8, 9, 2, 10, 12, 7, 4, 11], str, end = 8, 9

Output : [6, 3, 1, 8, 9, 2, 10, 7, 12, 4, 11]

Explanation : 12, 7 are reversed in list to 7, 12.

Method #1 : Using reverse() + loop

In this example, sublist is extracted and reversed using reverse(). The loop is used next to replace range elements with reversed elements. 

Python3

# Python3 code to demonstrate working of
# Reversing a range
# Using reverse() + loop

# initializing list
test_list = [6, 3, 1, 8, 9, 2, 10, 12, 7, 4, 11]

# printing original list
print("The original list is : " + str(test_list))

# initializing range
strt, end = 3, 9

# reversing list and assigning the range
temp = test_list[strt:end]
temp.reverse()
for idx in range(strt, end):
    test_list[idx] = temp[idx - strt]

# printing result
print("Range reversed range list : " + str(test_list))

Output:

The original list is : [6, 3, 1, 8, 9, 2, 10, 12, 7, 4, 11]
Range reversed range list : [6, 3, 1, 7, 12, 10, 2, 9, 8, 4, 11]

Method #2 : Using list split() + slicing

The compact approach to solve this problem is to perform a reversal of range list using list split way of reversing slicing only the required range. 

Python3

# Python3 code to demonstrate working of
# Reversing a range
# Using list split + slicing

# initializing list
test_list = [6, 3, 1, 8, 9, 2, 10, 12, 7, 4, 11]

# printing original list
print("The original list is : " + str(test_list))

# initializing range
strt, end = 3, 9

# Third arg. of split with -1 performs reverse
test_list[strt:end] = test_list[strt:end][::-1]

# printing result
print("Range reversed range list : " + str(test_list))

Output:

The original list is : [6, 3, 1, 8, 9, 2, 10, 12, 7, 4, 11]
Range reversed range list : [6, 3, 1, 7, 12, 10, 2, 9, 8, 4, 11]